Injury Severity is a Key Contributor to Coagulation Dysregulation and Fibrinogen Consumption.

Background: Traumatic injury is a leading cause of death for those under the age of 45, with 40% occurring due to hemorrhage. Severe tissue injury and hypoperfusion lead to marked changes in coagulation, thereby preventing formation of a stable blood clot and increasing hemorrhage associated mortality. Objectives: We aimed to quantify changes in clot formation and mechanics occurring after traumatic injury and the relationship to coagulation kinetics, and fibrinolysis. Methods: Plasma was isolated from injured patients upon arrival to the emergency department. Coagulation kinetics and mechanics of healthy donors and patient plasma were compared with rheological, turbidimetric and thrombin generation assays. ELISA's were performed to determine tissue plasminogen activator (tPA) and D-dimer concentration, as fibrinolytic markers. Results: Sixty-three patients were included in the study. The median injury severity score (ISS) was 17, median age was 37.5 years old, and mortality rate was 30%. Rheological, turbidimetric and thrombin generation assays indicated that trauma patients on average, and especially deceased patients, exhibited reduced clot stiffness, increased fibrinolysis and reduced thrombin generation compared to healthy donors. Fibrinogen concentration, clot stiffness, D-dimer and tPA all demonstrated significant direct correlation to increasing ISS. Machine learning algorithms identified and highlighted the importance of clinical factors on determining patient outcomes. Conclusions: Viscoelastic and biochemical assays indicate significant contributors and predictors of mortality for improved patient treatment and therapeutic target detection. ESSENTIALS: Traumatic injury may lead to alterations in a patient's ability to form stable blood clotsA study was performed to assess how trauma severity affects coagulation kineticsKey alterations were observed in trauma patients, who exhibit weaker and slower forming clotsPaired with machine learning methods, the results indicate key aspects contributing to mortality.

Delayed cardiac tamponade secondary to blast injury from gunshot wound.

Penetrating injuries are recognized for the direct tissue damage, which is typically evident on physical examination. Secondary injuries resulting from kinetic energy transfer in the case of gunshot wounds (GSWs), often referred to as "blast injuries", may affect tissues distant to the ballistic trajectory and are often occult. We present a case of delayed cardiac tamponade resulting from secondary blast injury. The patient sustained a thoraco-abdominal GSW with entry adjacent to the cardiac box. An Advanced Trauma Life Support (ATLS)-guided assessment revealed intra-abdominal injuries necessitating operative intervention without evidence of cardiac injury. On post-operative day four, the patient developed chest pain, tachycardia, and shortness of breath. Imaging revealed a large pericardial effusion with cardiac tamponade. Emergent exploration revealed hemopericardium secondary to a bleeding epicardial hematoma without evidence of pericardial violation. Clinicians must maintain a high clinical suspicion for occult, indirect blast injuries which may be life-threatening.

Hyperfibrinolysis drives mechanical instabilities in a simulated model of trauma induced coagulopathy.

INTRODUCTION: Trauma induced coagulopathy (TIC) is common after severe trauma, increasing transfusion requirements and mortality among patients. TIC has several phenotypes, with primary hyperfibrinolysis being among the most lethal. We aimed to investigate the contribution of hypercoagulation, hemodilution, and fibrinolytic activation to the hyperfibrinolytic phenotype of TIC, by examining fibrin formation in a plasma-based model of TIC. We hypothesized that instabilities arising from TIC will be due primarily to increased fibrinolytic activation rather than hemodilution or tissue factor (TF) induced hypercoagulation. METHODS: The influence of TF, hemodilution, fibrinogen consumption, tissue plasminogen activator (tPA), and the antifibrinolytic tranexamic acid (TXA) on plasma clot formation and structure were examined using rheometry, optical properties, and confocal microscopy. These were then compared to plasma samples from trauma patients at risk of developing TIC. RESULTS: Combining TF-induced clot formation, 15 % hemodilution, fibrinogen consumption, and tPA-induced fibrinolysis, the clot characteristics and hyperfibrinolysis were consistent with primary hyperfibrinolysis. TF primarily increased fibrin polymerization rates and reduced fiber length. Hemodilution decreased clot optical density but had no significant effect on mechanical clot stiffness. TPA addition induced primary clot lysis as observed mechanically and optically. TXA restored mechanical clot formation but did not restore clot structure to control levels. Patients at risk of TIC showed increased clot formation, and lysis like that of our simulated model. CONCLUSIONS: This simulated TIC plasma model demonstrated that fibrinolytic activation is a primary driver of instability during TIC and that clot mechanics can be restored, but clot structure remains altered with TXA treatment.

An Urgent Need for a Common Framework for the Articulation, Design and Reporting of Surgical System Strengthening Interventions Comment on "Improving Access to Surgery Through Surgical Team Mentoring - Policy Lessons From Group Model Building With Local Stakeholders in Malawi".

Nearly 60% of the world's inhabitants lack access to timely, safe, and ffordable emergency and essential surgical, anesthetic, and obstetric (SAO) services when needed. Although acknowledged as an important step in resolving this disparity, situation analysis informed development of national surgical, obstetric and anesthesia plans (NSOAPs) has not been performed widely. There are even fewer published examples of NSOAP driven SAO system vulnerability resolving policy interventions, potentially hindering broader acceptance and drafting. Thus, there is urgent need for alignment of academic global surgery activities through a common framework for SAO strengthening intervention articulation, design and reporting which can be informed by the Malawian experience and others. This is a logical next step in the evolution of surgical system science as we move towards the articulation of actionable inequity resolving interventions through stakeholder engagement embedded in a plan-do-study-act (PDSA) model for iterative refinement of strengthening policies.

Delayed presentation of a pneumatic nail gun injury to the right ventricle without circulatory compromise.

Delayed presentation of penetrating cardiac injuries is exceedingly rare due to the observed near 100% pre-hospital mortality. We describe a case of a patient who presented for evaluation nearly 24 h after sustaining a self-inflicted pneumatic nail gun injury to the right ventricular outflow tract. Remarkably, the patient had no evidence of hemodynamic compromise. This case highlights the importance of maintaining a high index of suspicion for cardiac injury with penetrating trauma to the cardiac box regardless of presenting signs and symptoms, and the value of adhering to advanced trauma life support principles.

A granular analysis of service delivery for surgical system strengthening: Application of the Lancet indicators for policy development in Colombia.

Background: The Lancet Commission on Global Surgery (LCoGS) surgical indicators have given the surgical community metrics for objectively characterizing the disparity in access to surgical healthcare. However, aggregate national statistics lack sufficient specificity to inform strengthening plans at the community level. We performed a second-stage analysis of Colombian surgical system service delivery to inform the development of resource- and context-sensitive interventions to inform a revision of the Decennial Public Health Plan for access inequity resolution. Methods: Data from the year 2016 to inform total operative volume (TOV) and 30-day non-risk adjusted peri-operative mortality (POMR) were collected from the Colombian national health information system. TOV and POMR were sub-characterized by demographics, urgency, service line, disease pathology and facility location. Findings: In 2016, aggregate national mortality was 0·87%, while mortality attributable to elective and emergency surgery was 0·73% and 1·30%, respectively. The elderly experienced a 5·6-fold higher mortality, with 4·2% undergoing an operation within 30 days of dying. Individuals undergoing hepatobiliary, thoracic, cardiac, and neurosurgical operations experienced the highest mortality rates while obstetrics, general surgery, orthopaedics, and urology performed the largest procedure volume. Finally, analysis of operation and service line specific POMR reveals opportunities for improvement. Interpretation: This granular second-stage analysis provides actionable data which is fundamental to the development of resource and context-sensitive interventions to address gaps and inequities in surgical system service delivery. Furthermore, this analysis validates the modeling underlying development of the LCoGS indicators. These data will inform the assessment of implementation priorities and revision of the Colombian Decennial Public Health Plan. Funding: None.

A longitudinal surgical systems strengthening research program for medical students: the exploration of a model for global health education.

BACKGROUND: In response to the staggering global burden of conditions requiring emergency and essential surgery, the development of international surgical system strengthening (SSS) is fundamental to achieving universal, timely, quality, and affordable surgical care. Opportunity exists in identifying optimal collaborative processes that both promote global surgery research and SSS, and include medical students. This study explores an education model to engage students in academic global surgery and SSS via institutional support for longitudinal research. OBJECTIVES: We set out to design a program to align global health education and longitudinal health systems research by creating an education model to engage medical students in academic global surgery and SSS. PROGRAM DESIGN AND IMPLEMENTATION: In 2015, medical schools in the United States and Colombia initiated a collaborative partnership for academic global surgery research and SSS. This included development of two longitudinal academic tracks in global health medical education and academic global surgery, which we differentiated by level of institutional resourcing. Herein is a retrospective evaluation of the first two years of this program by using commonly recognized academic output metrics. MAIN ACHIEVEMENTS: In the first two years of the program, there were 76 total applicants to the two longitudinal tracks. Six of the 16 (37.5%) accepted students selected global surgery faculty as mentors (Acute Care Surgery faculty participating in SSS with Colombia). These global surgery students subsequently spent 24 total working weeks abroad over the two-year period participating in culminating research experiences in SSS. As a quantitative measure of the program's success, the students collectively produced a total of twenty scholarly pieces in the form of accepted posters, abstracts, podium presentations, and manuscripts in partnership with Colombian research mentors. POLICY IMPLICATIONS: The establishment of scholarly global health education and research tracks has afforded our medical students an active role in international SSS through participation in academic global surgery research. We propose that these complementary programs can serve as a model for disseminated education and training of the future global systems-aware surgeon workforce with bidirectional growth in south and north regions with traditionally under-resourced SSS training programs.

Assessment of Cervical Cancer Prevention and Treatment Infrastructure in Belize.

PURPOSE: Belize has one of the highest cervical cancer burdens among Latin American and Caribbean countries, despite the implementation of national policies to increase access to prevention and treatment services. This study evaluates the policies, infrastructure, and workforce of the cervical cancer management system in Belize to inform capacity building efforts. METHODS: In 2018, health facility assessments were conducted across all six districts of Belize at the national pathology facility and 12 public facilities identified as critical to cervical cancer control. Human and infrastructure resource availability and existing policies related to cervical cancer screening and treatment services were assessed through a structured instrument. RESULTS: The public cervical cancer screening workforce in Belize consists of 75 primary care nurses and physicians-one per 1,076 screening-eligible women, with 44% conducting rural outreach. All districts have at least one screening facility, but 50% perform screening services only once per week. Colposcopy and loop electrical excision procedures are available in three and four districts, respectively; radical hysterectomy and chemotherapy are available in two districts; and radiation therapy is unavailable. Of essential pathology equipment, 38.5% were present and functional, 23% were present but nonfunctional, and 38.5% were unavailable. Additionally, 35% of supplies were unavailable at the time of assessment, and 75% were unavailable at least once in the 12 months before assessment. CONCLUSION: Public-sector cervical cancer management services differ among districts of Belize, with tertiary service availability concentrated in the largest district. Screening, outreach, and pathology are limited mostly by resource availability. This study characterizes the current capacity of services in Belize and pinpoints health system components for future investment and capacity-building efforts.

Mesenteric venous thrombosis: A lethal complication of hyperglycemic crises.

PURPOSE: Although hyperglycemic crises can lead to a hypercoagulable state, few instances of associated mesenteric venous thrombosis (MVT) have been reported. Worsening abdominal pain in the context of shock requiring vasopressor support should prompt urgent further investigation. SUMMARY: A 44-year-old Hispanic male arrived at an emergency department with chief complaints of lethargy, polydipsia, and polyuria. His past medical history included type 2 diabetes, epilepsy, obesity, tobacco smoking, and noncompliance with his medications. On arrival the patient had a serum glucose concentration of >1,600 mg/dL, and hyperosmolar hyperglycemic syndrome (HHS) was diagnosed. The patient was admitted to the intensive care unit with respiratory failure and subsequently developed shock refractory to fluid resuscitation, necessitating vasopressor support. On hospital day 4, a computerized tomogram obtained for investigation of increasing abdominal tenderness revealed superior MVT and pneumatosis intestinalis. Despite an emergency laparotomy and enterectomy, the patient ultimately succumbed on hospital day 41 due to recurrent pneumonia complicated by acute respiratory distress syndrome and septic shock. CONCLUSION: Shock that is refractory to aggressive fluid resuscitation, necessitating pressor support, in the setting of HHS or diabetic ketoacidosis should prompt investigation for the underlying source of shock. Other etiologies, including hypovolemic, cardiogenic, and obstructive shock, should be considered; however, infection is the leading trigger of hyperglycemic crises. Although rarely reported, MVT should be considered in the diagnostic algorithm in the absence of an identified infectious source. Prompt investigation should include use of diagnostic modalities such as computed tomography to assess for MVT.

Use of the six core surgical indicators from the Lancet Commission on Global Surgery in Colombia: a situational analysis.

BACKGROUND: Surgical, anaesthetic, and obstetric (SAO) health-care system strengthening is needed to address the emergency and essential surgical care that approximately 5 billion individuals lack globally. To our knowledge, a complete, non-modelled national situational analysis based on the Lancet Commission on Global Surgery surgical indicators has not been done. We aimed to undertake a complete situation analysis of SAO system preparedness, service delivery, and financial risk protection using the core surgical indicators proposed by the Commission in Colombia, an upper-middle-income country. METHODS: Data to inform the six core surgical system indicators were abstracted from the Colombian national health information system and the most recent national health survey done in 2007. Geographical access to a Bellwether hospital (defined as a hospital capable of providing essential and emergency surgery) within 2 h was assessed by determining 2 h drive time boundaries around Bellwether facilities and the population within and outside these boundaries. Physical 2 h access to a Bellwether was determined by the presence of a motor vehicle suitable for individual transportation. The Department Administrativo Nacional de Estadística population projection for 2016 and 2018 was used to calculate the SAO provider density. Total operative volume was calculated for 2016 and expressed nationally per 100 000 population. The total number of postoperative deaths that occurred within 30 days of a procedure was divided by the total operative volume to calculate the all-cause, non-risk-adjusted postoperative mortality. The proportion of the population subject to impoverishing costs was calculated by subtracting the baseline number of impoverished individuals from those who fell below the poverty line once out-of-pocket payments were accounted for. Individuals who incurred out-of-pocket payments that were more than 10% of their annual household income were considered to have experienced catastrophic expenditure. Using GIS mapping, SAO system preparedness, service delivery, and cost protection were also contextualised by socioeconomic status. FINDINGS: In 2016, at least 7·1 million people (15·1% of the population) in Colombia did not have geographical access to SAO services within a 2 h driving distance. SAO provider density falls short of the Commission's minimum target of 20 providers per 100 000 population, at an estimated density of 13·7 essential SAO health-care providers per 100 000 population in 2018. Lower socioeconomic status of a municipality, as indicated by proportion of people enrolled in the subsidised insurance regime, was associated with a smaller proportion of the population in the municipality being within 2 h of a Bellwether facility, and the most socioeconomically disadvantaged municipalities often had no SAO providers. Furthermore, Colombian providers appear to be working at or beyond capacity, doing 2690-3090 procedures per 100 000 population annually, but they have maintained a relatively low median postoperative mortality of 0·74% (IQR 0·48-0·84). Finally, out-of-pocket expenses for indirect health-care costs were a key barrier to accessing surgical care, prompting 3·1 million (6·4% of the population) individuals to become impoverished and 9·5 million (19·4% of the population) individuals to incur catastrophic expenditures in 2007. INTERPRETATION: We did a non-modelled, indicator-based situation analysis of the Colombian SAO system, finding that it has not yet met, but is working towards achieving, the targets set by the Lancet Commission on Global Surgery. The observed interdependence of these indicators and correlation with socioeconomic status are consistent with well recognised factors and outcomes of social, health, and health-care inequity. The internal consistency observed in Colombia's situation analysis validates the use of the indicators and has now informed development of an early national SAO plan in Colombia, to set a data-informed stage for implementation and evaluation of timely, safe, and affordable SAO health care, within the National Public Health Decennial Plan, which is due in 2022. FUNDING: Zoll Medical.

Next Generation of Global Surgeons: Aligning Interest With Early Access to Global Surgery Education.

BACKGROUND: Although interest in global surgery is increasing among medical students,1 several questions remain unanswered such as: the association of demographics with said interest, the extent that global surgical burden education has been integrated into medical education, and the availability of global surgery electives. This study aimed to assess the current state of global surgery education in the United States (U.S.) to support recommendations for future curriculum development. MATERIALS AND METHODS: An anonymous online survey was distributed to medical students currently enrolled in the U.S. Descriptive data were compiled regarding interest in and access to global surgery programs; demographic data were analyzed using chi-squared testing for categorical variables. RESULTS: A total of 754 students from 18 medical schools throughout the U.S. responded to the survey. Only complete responses were included in final analysis (n = 658). Most of the respondents (66%) reported interest in global surgery, with a higher proportion of those interested being in their preclinical years. However, the majority (79%) reported that global surgery issues are rarely or never addressed in their required curriculum. Over half of respondents were unaware of whether their school even offers such programs. CONCLUSIONS: Although interest in global surgery is on the rise among medical students, results suggest that many currently lack exposure to global surgery concepts in their medical education. To that end, early exposure may be most effective during the preclinical years, so that the next generation may align global surgery participation with clinical aspirations, with the ultimate goal of addressing global disparities.

The National Surgical, Obstetric, and Anesthesia Plan (NSOAP): Recognition and Definition of an Empirically Evolving Global Surgery Systems Science Comment on "Global Surgery - Informing National Strategies for Scaling Up Surgery in Sub-Saharan Africa".

In 2015, the Lancet Commission on Global Surgery (LCoGS) working groups developed a National Surgical, Obstetric, and Anesthesia Plan (NSOAP) framework to guide national surgical system development globally predicated on six data points (indicators) which can assess surgical systems. Zambia as well as other subSaharan Africa (SSA) countries have forged ahead in designing and implementing interventions based on LCoGS indicators collected to inform NSOAP. Concurrently, the Zambian team and others have recognized the need for rigorous scientific inquiry to assess and iteratively improve upon the NSOAP process and outputs. Based on the Zambian experience, as well as that of ours in Colombia, we have identified "core principles" through convergent works which inform a scientific framework through which NSOAP can be evaluated. We propose that when contextualized, participatory action research (PAR) and dissemination and implementation science are methodologies upon which a robust framework can be developed to achieving objective and iterative NSOAP evaluation, and ultimately universal health coverage as envisioned by the World Health Organization (WHO).

Mortality after emergency surgery continues to rise after discharge in the elderly: Predictors of 1-year mortality.

BACKGROUND: It is known that emergency surgery in the elderly is associated with high short-term mortality, but longer-term outcomes are not well described. We hypothesized that 30-day mortality may underestimate the true operative mortality experienced in this cohort. The purposes of this study were to characterize postoperative mortality rates extending to 1 year and to identify preoperative predictors of 1 year mortality after emergency abdominal surgery. METHODS: We retrospectively reviewed the records of all patients older than 70 years who underwent emergency abdominal surgery at a major teaching hospital between 2006 and 2011. Demographics, preoperative physiology, prehospital status, body mass index, laboratory values, Charlson scores, comorbid conditions, American Society of Anesthesiologists classification, and operative details were recorded. The primary end point was 1-year mortality. Complementary log-log binary regression was used to determine independent predictors of death. Model discrimination was evaluated using the c statistic. RESULTS: A total of 390 patients met our inclusion criteria. The mean age was 79 years, and 56% were women. Postoperative mortality was 16.2% at 30 days and 32.5% at 1 year, reflecting a doubling of mortality over 11 months. Independent preoperative predictors of 1-year mortality were Charlson score of 4 or higher (hazard ratio [HR], 1.79; 95% confidence interval [CI], 1.38-2.34), American Society of Anesthesiologists class of 4 or higher (HR, 1.66; 95% CI, 1.22-2.21), albumin less than 3.5 (HR, 1.71; 95% CI, 1.31-2.28), and body mass index lower than 18.5 (HR, 3.36; 95% CI, 1.48-6.86). The c statistic was 0.81. CONCLUSION: The 1-year mortality after emergency surgery in the elderly is significantly higher than that at 30 days. We identified a constellation of preoperative clinical markers that were highly predictive of this poor late outcome. The presence of these findings in the emergency setting should prompt preoperative discussion about treatment goals and encourage surgeons to set realistic expectations about outcomes with the patient and family. Future studies will develop a clinical scoring tool that can be applied at the bedside to provide more effective counseling for this high-risk population. LEVEL OF EVIDENCE: Epidemiologic/prognostic study, level III; therapeutic study, level IV.

Sarcopenia and critical illness: a deadly combination in the elderly.

Sarcopenia is the age-associated loss of lean skeletal muscle mass. It is the result of multiple physiologic derangements, ultimately resulting in an insidious functional decline. Frailty, the clinical manifestation of sarcopenia and physical infirmity, is associated with significant morbidity and mortality in the elderly population. The underlying pathology results in a disruption of the individual's ability to tolerate internal and external stressors such as injury or illness. This infirmity results in a markedly increased risk of falls and subsequent morbidity and mortality from the resulting traumatic injury, as well as an inability to recover from medical insults, resulting in critical illness. The increasing prevalence of sarcopenia and critical illness in the elderly has resulted in a deadly intersection of disease processes. The lethality of this combination appears to be the result of altered muscle metabolism, decreased mitochondrial energetics needed to survive critical illness, and a chronically activated catabolic state likely mediated by tumor necrosis factor-α. Furthermore, these underlying derangements are independently associated with an increased incidence of critical illness, resulting in a progressive downward spiral. Considerable evidence has been gathered supporting the role of aggressive nutrition support and physical therapy in improving outcomes. Critical care practitioners must consider sarcopenia and the resulting frailty phenotype a comorbid condition so that the targeted interventions can be instituted and research efforts focused.

Spontaneous adrenal pheochromocytoma rupture complicated by intraperitoneal hemorrhage and shock.

MEN2A is a hereditary syndrome characterized by medullary thyroid carcinoma, hyperparathyroidism, and pheochromocytoma. Classically patients with a pheochromocytoma initially present with the triad of paroxysmal headaches, palpitations, and diaphoresis accompanied by marked hypertension. However, although reported as a rare presentation, spontaneous hemorrhage within a pheochromocytoma can present as an abdominal catastrophe. Unrecognized, this transformation can rapidly result in death. We report the only documented case of a thirty eight year old gentleman with MEN2A who presented to a community hospital with hemorrhagic shock and peritonitis secondary to an unrecognized hemorrhagic pheochromocytoma. The clinical course is notable for an inability to localize the source of hemorrhage during an initial damage control laparotomy that stabilized the patient sufficiently to allow emergent transfer to our facility, re-exploration for continued hemorrhage and abdominal compartment syndrome, and ultimately angiographic embolization of the left adrenal artery for control of the bleeding. Following recovery from his critical illness and appropriate medical management for pheochromocytoma, he returned for interval bilateral adrenal gland resection, from which his recovery was unremarkable. Our review of the literature highlights the high mortality associated with the undertaking of an operative intervention in the face of an unrecognized functional pheochromocytoma. This reinforces the need for maintaining a high index of suspicion for pheochromocytoma in similar cases. Our case also demonstrates the need for a mutimodal treatment approach that will often be required in these cases.

S-phase checkpoint genes safeguard high-fidelity sister chromatid cohesion.

Cohesion establishment and maintenance are carried out by proteins that modify the activity of Cohesin, an essential complex that holds sister chromatids together. Constituents of the replication fork, such as the DNA polymerase alpha-binding protein Ctf4, contribute to cohesion in ways that are poorly understood. To identify additional cohesion components, we analyzed a ctf4Delta synthetic lethal screen performed on microarrays. We focused on a subset of ctf4Delta-interacting genes with genetic instability of their own. Our analyses revealed that 17 previously studied genes are also necessary for the maintenance of robust association of sisters in metaphase. Among these were subunits of the MRX complex, which forms a molecular structure similar to Cohesin. Further investigation indicated that the MRX complex did not contribute to metaphase cohesion independent of Cohesin, although an additional role may be contributed by XRS2. In general, results from the screen indicated a sister chromatid cohesion role for a specific subset of genes that function in DNA replication and repair. This subset is particularly enriched for genes that support the S-phase checkpoint. We suggest that these genes promote and protect a chromatin environment conducive to robust cohesion.

Distinct chromosome segregation roles for spindle checkpoint proteins.

The spindle checkpoint plays a central role in the fidelity of chromosome transmission by ensuring that anaphase is initiated only after kinetochore-microtubule associations of all sister chromatid pairs are complete. In this study, we find that known spindle checkpoint proteins do not contribute equally to chromosome segregation fidelity in Saccharomyces cerevisiae. Loss of Bub1 or Bub3 protein elicits the largest effect. Analysis of Bub1p reveals the presence of two molecular functions. An N-terminal 608-amino acid (nonkinase) portion of the protein supports robust checkpoint activity, and, as expected, contributes to chromosome segregation. A C-terminal kinase-encoding segment independently contributes to chromosome segregation through an unknown mechanism. Both molecular functions depend on association with Bub3p. A 156-amino acid fragment of Bub1p functions in Bub3p binding and in kinetochore localization by one-hybrid assay. An adjacent segment is required for Mad1p binding, detected by deletion analysis and coimmunoprecipitation. Finally, overexpression of wild-type BUB1 or MAD3 genes leads to chromosome instability. Analysis of this activity indicates that the Bub3p-binding domain of Bub1p contributes to this phenotype through disruption of checkpoint activity as well as through introduction of kinetochore or spindle damage.