Risk Factors for Incident Polycystic Ovary Syndrome Diagnosis.

Objective: While highly prevalent, risk factors for incident polycystic ovary syndrome (PCOS) are poorly delineated. Using a population-based cohort, we sought to identify predictors of incident PCOS diagnosis. Materials and Methods: A matched case-control analysis was completed utilizing patients enrolled in Kaiser Permanente Washington from 2006 to 2019. Inclusion criteria included female sex, age 16-40 years, and ≥3 years of prior enrollment with ≥1 health care encounter. PCOS cases were identified using International Classification of Diseases codes. For each incident case (n = 2,491), 5 patients without PCOS (n = 12,455) were matched based on birth year and enrollment status. Potential risk factors preceding diagnosis included family history of PCOS, premature menarche, parity, race, weight gain, obesity, valproate use, metabolic syndrome, epilepsy, prediabetes, and types 1 and 2 diabetes. Potential risk factors for incident PCOS diagnosis were assessed with univariate and multivariable conditional logistic regressions. Results: Mean age of PCOS cases was 26.9 years (SD 6.8). PCOS cases, compared with non-PCOS, were more frequently nulliparous (70.9% versus 62.4%) and in the 3 years prior to index date were more likely to have obesity (53.8% versus 20.7%), metabolic syndrome (14.5% versus 4.3%), prediabetes (7.4% versus 1.6%), and type 2 diabetes (4.1% versus 1.7%) (p < 0.001 for all comparisons). In multivariable models, factors associated with higher risk for incident PCOS included the following: obesity (compared with nonobese) Class I-II (body-mass index [BMI], 30-40 kg/m2; odds ratio [OR], 3.8; 95% confidence interval [CI], 3.4-4.2), Class III (BMI > 40 kg/m2; OR, 7.5, 95% CI, 6.5-8.7), weight gain (compared with weight loss or maintenance) of 1-10% (OR, 1.7, 95% CI, 1.3-2.1), 10-20% (OR, 1.9; 95% CI, 1.5-2.4), and >20% (OR, 2.6; 95% CI, 1.9-3.6), prediabetes (OR, 2.7; 95% CI, 2.1-3.4), and metabolic syndrome (OR, 1.8: 95% CI, 1.5-2.1). Conclusion: Excess weight gain, obesity, and metabolic dysfunction may play a key role in the ensuing phenotypic expression of PCOS. Treatment and prevention strategies targeted at preventing weight gain in early reproductive years may help reduce the risk of this syndrome.

Data-driven automated classification algorithms for acute health conditions: applying PheNorm to COVID-19 disease.

OBJECTIVES: Automated phenotyping algorithms can reduce development time and operator dependence compared to manually developed algorithms. One such approach, PheNorm, has performed well for identifying chronic health conditions, but its performance for acute conditions is largely unknown. Herein, we implement and evaluate PheNorm applied to symptomatic COVID-19 disease to investigate its potential feasibility for rapid phenotyping of acute health conditions. MATERIALS AND METHODS: PheNorm is a general-purpose automated approach to creating computable phenotype algorithms based on natural language processing, machine learning, and (low cost) silver-standard training labels. We applied PheNorm to cohorts of potential COVID-19 patients from 2 institutions and used gold-standard manual chart review data to investigate the impact on performance of alternative feature engineering options and implementing externally trained models without local retraining. RESULTS: Models at each institution achieved AUC, sensitivity, and positive predictive value of 0.853, 0.879, 0.851 and 0.804, 0.976, and 0.885, respectively, at quantiles of model-predicted risk that maximize F1. We report performance metrics for all combinations of silver labels, feature engineering options, and models trained internally versus externally. DISCUSSION: Phenotyping algorithms developed using PheNorm performed well at both institutions. Performance varied with different silver-standard labels and feature engineering options. Models developed locally at one site also worked well when implemented externally at the other site. CONCLUSION: PheNorm models successfully identified an acute health condition, symptomatic COVID-19. The simplicity of the PheNorm approach allows it to be applied at multiple study sites with substantially reduced overhead compared to traditional approaches.

Incidence, prevalence, and trends in polycystic ovary syndrome diagnosis: a United States population-based study from 2006 to 2019.

BACKGROUND: Polycystic ovary syndrome is the most common endocrine disorder in women of reproductive age, yet US incidence estimates do not exist, and prevalence estimates vary widely. OBJECTIVE: A population-based US study estimated the incidence, prevalence, and trends of polycystic ovary syndrome by age, race and ethnicity, and diagnosing provider type. STUDY DESIGN: A retrospective cohort study of patients enrolled in Kaiser Permanente Washington from 2006 to 2019 was conducted. All members identified as female, aged 16 to 40 years with at least 3 years of enrollment and at least 1 healthcare encounter during that time, were eligible for inclusion. Individuals were excluded if they had a history of oophorectomy or hysterectomy. Polycystic ovary syndrome cases were identified using the International Classification of Diseases diagnosis codes (International Classification of Diseases, Ninth Revision, 256.4 or International Classification of Diseases, Tenth Revision, E28.2). Individuals with a polycystic ovary syndrome diagnosis before study entry were excluded from incidence rate estimations. The incidence rates were adjusted by age using direct standardization to the 2010 US census data. Temporal trends in incidence were assessed using weighted linear regression (overall) and Poisson regression (by age, race and ethnicity, and provider type). Prevalent cases were defined as patients with a polycystic ovary syndrome diagnosis at any time before the end of 2019. Medical record review of 700 incident cases diagnosed in 2011-2019 was performed to validate incident cases identified by International Classification of Diseases codes using the Rotterdam criteria. RESULTS: Among 177,527 eligible patients who contributed 586,470 person-years, 2491 incident polycystic ovary syndrome cases were identified. The mean age at diagnosis was 26.9 years, and the mean body mass index was 31.6 kg/m2. Overall incidence was 42.5 per 10,000 person-years; the rates were similar over time but increased in individuals aged 16 to 20 years from 31.0 to 51.9 per 10,000 person-years (P=.01) and decreased among those aged 26 to 30 years from 82.8 to 45.0 per 10,000 person-years (P=.02). A small decreasing temporal trend in incidence rates was only observed among non-Hispanic White individuals (P=.01). The incidence rates by diagnosing provider type varied little over time. Among the 58,241 patients who contributed person-time in 2019, 3036 (5.2%) had a polycystic ovary syndrome International Classification of Diseases diagnosis code; the prevalence was the highest among the Hawaiian and Pacific Islander group (7.6%) followed by Native American and Hispanic groups. Medical record review classified 60% as definite or probable incident, 14% as possible incident, and 17% as prevalent polycystic ovary syndrome. The overall positive predictive value of polycystic ovary syndrome International Classification of Diseases diagnosis code for identifying definite, probable, or possible incident polycystic ovary syndrome was 76% (95% confidence interval, 72%-79%). CONCLUSION: Among a cohort of nonselected females in the United States, we observed stable rates of incident polycystic ovary syndrome diagnoses over time. The incidence of polycystic ovary syndrome was 4- to 5-fold greater than reported for the United Kingdom. The prevalence of polycystic ovary syndrome (5.2%) was almost double before the published US estimates (2.9%) based on the International Classification of Diseases codes. Race and ethnicity and provider type did not seem to have a major impact on temporal rates. Incident diagnoses increased over time in younger and decreased in older age groups, perhaps related to shifting practice patterns with greater awareness among practitioners of the impact of polycystic ovary syndrome on long-term health outcomes and improved prevention efforts. Moreover, increasing obesity rates may be a factor driving the earlier ages at diagnosis.

Family Caregiver Needs and Preferences for Virtual Training to Manage Behavioral and Psychological Symptoms of Dementia: Interview Study.

BACKGROUND: Behavioral and psychological symptoms of dementia (BPSD) are associated with increased stress, burden, and depression among family caregivers of people with dementia. STAR-Caregivers Virtual Training and Follow-up (STAR-VTF) is adapted from an evidence-based, in-person program that trains family caregivers to manage BPSD. We used a human-centered design approach to obtain feedback from family caregivers about STAR-VTF. The program will be evaluated using a pragmatic randomized trial. OBJECTIVE: The objective of the study was to understand the needs of family caregivers for improving BPSD management and the extent to which caregivers perceived that STAR-VTF could address those needs. METHODS: Between July and September 2019, we conducted 15 semistructured interviews with family caregivers of people with dementia who receive care at Kaiser Permanente Washington in the Seattle metropolitan area. We identified participants from electronic health records, primarily based on a prescription for antipsychotic medication for the person with dementia (a proxy for caregivers dealing with BPSD). We showed caregivers low-fidelity prototypes of STAR-VTF online self-directed materials and verbally described potential design elements. We obtained caregiver feedback on these elements, focusing on their needs and preferences and perceived barriers to using STAR-VTF. We used a hybrid approach of inductive and deductive coding and aggregated codes to develop themes. RESULTS: The idea of a virtual training program for learning to manage BPSD appealed to caregivers. They said health care providers did not provide adequate education in the early disease stages about the personality and behavior symptoms that can affect people with dementia. Caregivers found it unexpected and frustrating when the person with dementia began experiencing BPSD, symptoms they felt unprepared to manage. Accordingly, caregivers expressed a strong desire for the health care organization to offer programs such as STAR-VTF much sooner. Caregivers had already put considerable effort into problem solving challenging behaviors. They anticipated deriving less value from STAR-VTF at that point. Nonetheless, many were interested in the virtual aspect of the training due to the convenience of receiving help from home and the perception that help from a virtual program would be timelier than traditional service modalities (eg, face to face). Given caregivers' limited time, they suggested dividing the STAR-VTF content into chunks to review as time permitted. Caregivers were interested in having a STAR-VTF provider for additional support in managing challenging behaviors. Caregivers reported a preference for having the same coach for the program duration. CONCLUSIONS: Caregivers we interviewed would likely accept a virtual training program such as STAR-VTF to obtain information about BPSD and receive help managing it. Family caregivers anticipated deriving more value if STAR-VTF was offered earlier in the disease course.

Taking the Next Steps in Regenerative Rehabilitation: Establishment of a New Interdisciplinary Field.

The growing field of regenerative rehabilitation has great potential to improve clinical outcomes for individuals with disabilities. However, the science to elucidate the specific biological underpinnings of regenerative rehabilitation-based approaches is still in its infancy and critical questions regarding clinical translation and implementation still exist. In a recent roundtable discussion from International Consortium for Regenerative Rehabilitation stakeholders, key challenges to progress in the field were identified. The goal of this article is to summarize those discussions and to initiate a broader discussion among clinicians and scientists across the fields of regenerative medicine and rehabilitation science to ultimately progress regenerative rehabilitation from an emerging field to an established interdisciplinary one. Strategies and case studies from consortium institutions-including interdisciplinary research centers, formalized courses, degree programs, international symposia, and collaborative grants-are presented. We propose that these strategic directions have the potential to engage and train clinical practitioners and basic scientists, transform clinical practice, and, ultimately, optimize patient outcomes.

Contextual factors associated with consistent condom use and condom self-efficacy amongst African asylum seekers and refugees in Hong Kong.

BACKGROUND: Hong Kong has no systematic domestic policies committed to the rights of asylum-seekers and refugees (ASRs). This study explores the sexual health behaviours and social inequities amongst African ASRs in Hong Kong. METHODS: A cross-sectional survey of African ASRs was conducted through three local non-governmental organizations in 2013. A logistic model was used to test the interactions and relationship between the respondents' consistent condom use and contextual antecedents, socio-demographic factors, psychosocial factors and condom self-efficacy (CSE) score. RESULTS: 371 adult African ASRs were recruited. In the previous month, 35% and 38% of participants consistently had used condoms with regular and casual sexual partners respectively. However, less than 50% perceived no risk of HIV/STIs and less than 60% reported not knowing how to access sexual health screening. Consistent condom use was less likely among African ASRs who were married (adjusted odds ratio (aOR) = 0.10), used recreational drugs (aOR = 0.11) or were unsure of their sexual orientation (aOR = 0.05) and was positively associated with higher CSE scores (aOR = 1.09) Pre-migration determinants and lifestyle determinants accounted for most of the variance in the model. CONCLUSION: The inconsistent condom use makes African ASRs vulnerable to HIV/STIs. Tailored interventions are needed to address the associated determinants and inequities amongst African ASRs living in Hong Kong.

Mental health of African asylum-seekers and refugees in Hong Kong: using the social determinants of health framework.

BACKGROUND: Hong Kong is non-signatory to the 1951 Refugee Convention and its 1967 Protocol, and has no systematic domestic policies committed to the rights of asylum-seekers and refugees (ASRs). This creates a tenuous setting for African ASRs there. This study explored how mapped social determinates of health has impacted the mental health and wellbeing of African ASR's in Hong Kong. METHODS: A cross-sectional survey was carried out with 374 African ASRs. The survey comprised of: (a) socio-demographics; (b) health status; (c) health behaviours; and, (d) social experiences. Associations between social determinants of health and depression screen were explored and multivariable regression analysis was conducted. RESULTS: Majority of participants were 18-37 years old (79.7%), male (77.2%), single (66.4%) and educated (60.9% high school and above). Over a third (36.1%) screened positive for depression. Analyses revealed that living with family reduced the odds of a positive depression screen (OR = 0.25, 95%CI = 0.07-0.88). Those perceiving their health to be "Poor" were 5.78 times as likely to be screened for depression. Additionally, those with higher scores on the discrimination scale were more likely to have positive depression screen (OR = 1.17, 95%CI = 1.10-1.24). CONCLUSION: A significant proportion of African ASRs in Hong Kong exhibits depressive symptoms. A complex interaction combining both social and perceptions of health and discrimination in the host society is likely exacerbated by their ASR status. The use of community support groups or even re-examination of the family reunification laws could improve the mental health and wellbeing of African ASRs in Hong Kong.

A lost tribe in the city: health status and needs of African asylum seekers and refugees in Hong Kong.

BACKGROUND: Hong Kong's resistance to be a signatory of the 1951 Geneva Convention and lack of domestic policies in this area has resulted in restrictions on access to healthcare amongst asylum seekers and refugees (ASRs). Using social determinants of health framework this study sought to identify health practices, problems and needs of African ASRs in Hong Kong. METHODS: A cross-sectional survey comprising of six domains including health status, health-seeking behaviour and social experience targeted at adult African ASRs in Hong Kong was conducted through three local non-governmental organisations between February and April 2013. Outpatient care and inpatient care in the past 12 months were used as proxy measures of general and severe ill health respectively. Associations between the determinants of health factors with general or severe health was explored through logistic regressions. RESULTS: Majority of 374 participants were young, single, educated males having been in Hong Kong for over 5 years. A third of ARS (36.1 %) screened positive for depression. Most reported problems related to basic necessities (64.7-78.6 %) and access to health services (72.2 %). ASRs with relatively less education, health awareness or higher risk behaviours were less likely to have obtained outpatient or inpatient services. African ASRs reporting problems with case officers (aOR = 2.80; 95 % CI = 1.35-5.79) or illness in the past 30 days (aOR = 6.00; 95 % CI = 2.94-12.25) were more likely to report general ill health. Similarly, problems with the case officers (aOR = 3.76; 95 % CI = 1.97-7.18) and self-reported illness in the past 30 days (a​OR = 3.32; 95 % CI= 1.68-6.57) were also significantly associated with severe ill health. At the health system level, those who reported experiencing difficulties accessing the medical services in Hong Kong are 3.29 (95 % CI = 1.48-7.31) and 4.12 (95 % CI = 1.73-9.79) times as likely to report general and severe ill health respectively. CONCLUSION: The host government should have moral and ethical obligations to attend to the health needs of ASRs. Evidently a number of structural and health system factors have significantly impacted the health of African ASRs in Hong Kong. Changes to current policies regarding how African ASRs are handled whilst in Hong Kong but, more immediately, improvements in healthcare access are needed.

Molecular architecture of a eukaryotic translational initiation complex.

The last step in eukaryotic translational initiation involves the joining of the large and small subunits of the ribosome, with initiator transfer RNA (Met-tRNA(i)(Met)) positioned over the start codon of messenger RNA in the P site. This step is catalyzed by initiation factor eIF5B. We used recent advances in cryo-electron microscopy (cryo-EM) to determine a structure of the eIF5B initiation complex to 6.6 angstrom resolution from <3% of the population, comprising just 5143 particles. The structure reveals conformational changes in eIF5B, initiator tRNA, and the ribosome that provide insights into the role of eIF5B in translational initiation. The relatively high resolution obtained from such a small fraction of a heterogeneous sample suggests a general approach for characterizing the structure of other dynamic or transient biological complexes.

The ribosome triggers the stringent response by RelA via a highly distorted tRNA.

The bacterial stringent response links nutrient starvation with the transcriptional control of genes. This process is initiated by the stringent factor RelA, which senses the presence of deacylated tRNA in the ribosome as a symptom of amino-acid starvation to synthesize the alarmone (p)ppGpp. Here we report a cryo-EM study of RelA bound to ribosomes bearing cognate, deacylated tRNA in the A-site. The data show that RelA on the ribosome stabilizes an unusual distorted form of the tRNA, with the acceptor arm making contact with RelA and far from its normal location in the peptidyl transferase centre.

Unusual base pairing during the decoding of a stop codon by the ribosome.

During normal translation, the binding of a release factor to one of the three stop codons (UGA, UAA or UAG) results in the termination of protein synthesis. However, modification of the initial uridine to a pseudouridine (Ψ) allows efficient recognition and read-through of these stop codons by a transfer RNA (tRNA), although it requires the formation of two normally forbidden purine-purine base pairs. Here we determined the crystal structure at 3.1 Å resolution of the 30S ribosomal subunit in complex with the anticodon stem loop of tRNA(Ser) bound to the ΨAG stop codon in the A site. The ΨA base pair at the first position is accompanied by the formation of purine-purine base pairs at the second and third positions of the codon, which show an unusual Watson-Crick/Hoogsteen geometry. The structure shows a previously unsuspected ability of the ribosomal decoding centre to accommodate non-canonical base pairs.

Elongation factor G bound to the ribosome in an intermediate state of translocation.

A key step of translation by the ribosome is translocation, which involves the movement of messenger RNA (mRNA) and transfer RNA (tRNA) with respect to the ribosome. This allows a new round of protein chain elongation by placing the next mRNA codon in the A site of the 30S subunit. Translocation proceeds through an intermediate state in which the acceptor ends of the tRNAs have moved with respect to the 50S subunit but not the 30S subunit, to form hybrid states. The guanosine triphosphatase (GTPase) elongation factor G (EF-G) catalyzes the subsequent movement of mRNA and tRNA with respect to the 30S subunit. Here, we present a crystal structure at 3 angstrom resolution of the Thermus thermophilus ribosome with a tRNA in the hybrid P/E state bound to EF-G with a GTP analog. The structure provides insights into structural changes that facilitate translocation and suggests a common GTPase mechanism for EF-G and elongation factor Tu.

Crystal structure of a bioactive pactamycin analog bound to the 30S ribosomal subunit.

Biosynthetically and chemically derived analogs of the antibiotic pactamycin and de-6-methylsalicylyl (MSA)-pactamycin have attracted recent interest as potential antiprotozoal and antitumor drugs. Here, we report a 3.1-Å crystal structure of de-6-MSA-pactamycin bound to its target site on the Thermus thermophilus 30S ribosomal subunit. Although de-6-MSA-pactamycin lacks the MSA moiety, it shares the same binding site as pactamycin and induces a displacement of nucleic acid template bound at the E-site of the 30S. The structure highlights unique interactions between this pactamycin analog and the ribosome, which paves the way for therapeutic development of related compounds.

The six dimensions of wellness and cognition in aging adults.

OBJECTIVE: Examine how wellness in six dimensions (occupational, social, intellectual, physical, emotional, and spiritual) protects cognition in aging adults. BACKGROUND: cognitive impairment increases with age. Baby boomers represent a significant percent of the population at risk for cognitive impairment. Cognitive impairment has a negative impact on nursing resources, health care finances, patient mortality, and quality of life. Wellness and prevention is one focus of Institute of Medicine's vision for the future of nursing. METHOD: Literature was retrieved from Cumulative Index to Nursing and Allied Health Literature and MEDLINE. Research that examined the affect of wellness in each of the six dimensions on cognition in older adults was included. RESULTS: One or more of the following may protect cognition in aging: midlife occupation complexity, marriage, social networks, formal education, intellectual activities, physical activity, healthy nutrition, motivational ability, purpose in life, and spirituality. CONCLUSION: Wellness in one or more of the six dimensions may protect cognition in aging. The cognitive protective benefits may increase when wellness in more than one dimension is demonstrated. High wellness in one dimension may protect cognition by compensating for low wellness in another dimension. The interconnectedness of each of the dimensions signifies the importance of evaluating older adults holistically. Wellness throughout the life span may result in improved cognition in aging. APPLICATION: Future research is needed to examine the relationship between the six dimensions of wellness and cognition, and to determine if one dimension of wellness is a significant predictor of cognitive health in aging adults.

Decoding in the absence of a codon by tmRNA and SmpB in the ribosome.

In bacteria, ribosomes stalled at the end of truncated messages are rescued by transfer-messenger RNA (tmRNA), a bifunctional molecule that acts as both a transfer RNA (tRNA) and a messenger RNA (mRNA), and SmpB, a small protein that works in concert with tmRNA. Here, we present the crystal structure of a tmRNA fragment, SmpB and elongation factor Tu bound to the ribosome at 3.2 angstroms resolution. The structure shows how SmpB plays the role of both the anticodon loop of tRNA and portions of mRNA to facilitate decoding in the absence of an mRNA codon in the A site of the ribosome and explains why the tmRNA-SmpB system does not interfere with normal translation.

Crystal structure of the hybrid state of ribosome in complex with the guanosine triphosphatase release factor 3.

Protein release factor 3 (RF3), a guanosine triphosphatase, binds to ribosome after release of the nascent peptide and promotes dissociation of the class I release factors during the termination of protein synthesis. Here we present the crystal structure of the 70S ribosome with RF3 in the presence of a nonhydrolyzable GTP analogue, guanosine 5'-ß,γ-methylenetriphosphate (GDPCP), refined to 3.8 Å resolution. The structure shows that the subunits of the ribosome are rotated relative to each other compared to the canonical state, resulting in a P/E hybrid state for the transfer RNA. The substantial conformational rearrangements in the complex are described and suggest how RF3, by stabilizing the hybrid state of the ribosome, facilitates the dissociation of class I release factors.

How mutations in tRNA distant from the anticodon affect the fidelity of decoding.

The ribosome converts genetic information into protein by selecting aminoacyl tRNAs whose anticodons base-pair to an mRNA codon. Mutations in the tRNA body can perturb this process and affect fidelity. The Hirsh suppressor is a well-studied tRNA(Trp) harboring a G24A mutation that allows readthrough of UGA stop codons. Here we present crystal structures of the 70S ribosome complexed with EF-Tu and aminoacyl tRNA (native tRNA(Trp), G24A tRNA(Trp) or the miscoding A9C tRNA(Trp)) bound to cognate UGG or near-cognate UGA codons, determined at 3.2-Å resolution. The A9C and G24A mutations lead to miscoding by facilitating the distortion of tRNA required for decoding. A9C accomplishes this by increasing tRNA flexibility, whereas G24A allows the formation of an additional hydrogen bond that stabilizes the distortion. Our results also suggest that each native tRNA will adopt a unique conformation when delivered to the ribosome that allows accurate decoding.

A comparison of adult and adolescent rat behavior in operant learning, extinction, and behavioral inhibition paradigms.

Poor self-control, lack of inhibition, and impulsivity contribute to the propensity of adolescents to engage in risky or dangerous behaviors. Brain regions (e.g., prefrontal cortex) involved in impulse-control, reward-processing, and decision-making continue to develop during adolescence, raising the possibility that an immature brain contributes to dangerous behavior during adolescence. However, very few validated animal behavioral models are available for behavioral neuroscientists to explore the relationship between brain development and behavior. To that end, a valid model must be conducted in the relatively brief window of adolescence and not use manipulations that potentially compromise development. The present experiments used three operant arrangements to assess whether adolescent rats differ from adults in measures of learning, behavioral inhibition, and impulsivity, within the aforementioned time frame without substantial food restriction. In Experiment 1, separate squads of rats were trained to lever-press and then transitioned to two types of extinction. Relative to their baselines, adolescent rats responded more during extinction than adults, suggesting that they were less sensitive to the abolishment of the reinforcement contingency. Experiment 2 demonstrated similar age-related differences during exposure to a differential reinforcement of low rates schedule, a test of behavioral inhibition. Lastly, in Experiment 3, adolescent's responding decreased more slowly than adults during exposure to a resetting delay of reinforcement schedule, suggesting impaired self-control. Results from these experiments suggest that adolescents exhibit impaired learning, behavioral inhibition and self-control, and in concert with recent reports, provide researchers with three behavioral models to more fully explore neurobiology of risk-taking behavior in adolescence.

The mechanism for activation of GTP hydrolysis on the ribosome.

Protein synthesis requires several guanosine triphosphatase (GTPase) factors, including elongation factor Tu (EF-Tu), which delivers aminoacyl-transfer RNAs (tRNAs) to the ribosome. To understand how the ribosome triggers GTP hydrolysis in translational GTPases, we have determined the crystal structure of EF-Tu and aminoacyl-tRNA bound to the ribosome with a GTP analog, to 3.2 angstrom resolution. EF-Tu is in its active conformation, the switch I loop is ordered, and the catalytic histidine is coordinating the nucleophilic water in position for inline attack on the γ-phosphate of GTP. This activated conformation is due to a critical and conserved interaction of the histidine with A2662 of the sarcin-ricin loop of the 23S ribosomal RNA. The structure suggests a universal mechanism for GTPase activation and hydrolysis in translational GTPases on the ribosome.

Modification of 16S ribosomal RNA by the KsgA methyltransferase restructures the 30S subunit to optimize ribosome function.

All organisms incorporate post-transcriptional modifications into ribosomal RNA, influencing ribosome assembly and function in ways that are poorly understood. The most highly conserved modification is the dimethylation of two adenosines near the 3' end of the small subunit rRNA. Lack of these methylations due to deficiency in the KsgA methyltransferase stimulates translational errors during both the initiation and elongation phases of protein synthesis and confers resistance to the antibiotic kasugamycin. Here, we present the X-ray crystal structure of the Thermus thermophilus 30S ribosomal subunit lacking these dimethylations. Our data indicate that the KsgA-directed methylations facilitate structural rearrangements in order to establish a functionally optimum subunit conformation during the final stages of ribosome assembly.