A pilot study to record visual evoked potentials during prone spine surgery using the SightSaver™ photic visual stimulator.

This is a pilot study to assess the clinical safety and efficacy of recording real-time flash visual evoked potentials (VEPs) using the SightSaver TM Visual Stimulator mask during prone spine surgery. A prospective, observational pilot study. Twenty patients presenting for spine surgery (microdiscectomy, 1-2 level lumbar fusion, or > 2 levels thoraco-lumbar fusion) were enrolled. The SightSaver™ Visual Stimulator™ was used to elicit VEPs throughout surgery. Somatosensory evoked potentials (SSEPs) were simultaneously recorded. All patients underwent general anesthesia with a combination of intravenous and inhaled agents. The presence, absence, and changes in VEP were qualitatively analyzed. Reproducible VEPs were elicited in 18/20 patients (36/40 eyes). VEPs were exquisitely sensitive to changes in anesthesia and decayed with rising MAC of isoflurane and/or N2O. Decrements in VEPs were observed without concomitant changes in SSEPs. The mask was simple to apply and use and was not associated with adverse effects. The SightSaver™ mask represents an emerging technology for monitoring developing visual insults during surgery. The definitive applications remain to be determined, but likely include use in select patients and/or surgeries. Here, we have validated the device as safe and effective, and show that VEPs can be recorded in real time under general anesthesia in the prone position. Future studies should be directed towards understanding the ideal anesthetic regimen to facilitate stable VEP recording during prone spine surgery.

Pregnancy history, coronary artery calcification and bone mineral density in menopausal women.

OBJECTIVE: This study examined relationships, by pregnancy histories, between bone mineral density (BMD) and coronary artery calcification (CAC) in postmenopausal women. METHODS: Forty women identified from their medical record as having pre-eclampsia (PE) were age/parity-matched with 40 women having a normotensive pregnancy (NP). Vertebral (T4-9) BMD and CAC were assessed by quantitative computed tomography in 73 (37 with PE and 36 with NP) of the 80 women. Analyses included linear regression using generalized estimating equations. RESULTS: Women averaged 59 years of age and 35 years from the index pregnancy. There were no significant differences in cortical, trabecular or central BMD between groups. CAC was significantly greater in the PE group (p = 0.026). In multivariable analysis, CAC was positively associated with cortical BMD (p = 0.001) and negatively associated with central BMD (p = 0.036). There was a borderline difference in the association between CAC and central BMD by pregnancy history (interaction, p = 0.057). CONCLUSIONS: Although CAC was greater in women with a history of PE, vertebral BMD did not differ between groups. However, both cortical and central BMD were associated with CAC. The central BMD association was marginally different by pregnancy history, suggesting perhaps differences in underlying mechanisms of soft tissue calcification.

Factor XIII cotreatment with hemostatic agents in hemophilia A increases fibrin α-chain crosslinking.

Essentials Factor XIII (FXIII)-mediated fibrin crosslinking is delayed in hemophilia. We determined effects of FXIII cotreatment with hemostatic agents on clot parameters. FXIII cotreatment accelerated FXIII activation and crosslinking of fibrin and α2 -antiplasmin. These data provide biochemical rationale for FXIII cotreatment in hemophilia. SUMMARY: Background Hemophilia A results from the absence, deficiency or inhibition of factor VIII. Bleeding is treated with hemostatic agents (FVIII, recombinant activated FVII [rFVIIa], anti-inhibitor coagulation complex [FEIBA], or recombinant porcine FVIII [rpFVIII]). Despite treatment, some patients have prolonged bleeding. FXIII-A2 B2 (FXIII) is a protransglutaminase. During clot contraction, thrombin-activated FXIII (FXIIIa) crosslinks fibrin and α2 -antiplasmin, which promotes red blood cell retention and increases clot stability and weight. We hypothesized that FXIII cotreatment in hemophilia would accelerate FXIII activation, leading to increased fibrin crosslinking. Methods FVIII-deficient plasma and whole blood were clotted with or without hemostatic agents (FVIII, rFVIIa, FEIBA, or recombinant B-domain-deleted porcine FVIII [rpFVIII]) and/or FXIII. The effects on FXIII activation, thrombin generation, fibrin and α2 -antiplasmin crosslinking, clot formation and clot weight were measured by western blotting, calibrated automated thrombography, thromboelastography, and clot contraction assays. Results As compared with FVIII-treated hemophilic plasma, FVIII + FXIII cotreatment accelerated FXIIIa formation without increasing thrombin generation. As compared with buffer-treated or FXIII-treated hemophilic plasma, FVIII treatment and FVIII + FXIII cotreatment increased the generation and amount of crosslinked fibrin, including α-chain-rich high molecular weight species and crosslinked α2 -antiplasmin. In the presence of FVIII inhibitors, as compared with hemostatic treatments (rFVIIa, FEIBA, or rpFVIII) alone, FXIII cotreatment increased whole blood clot weight. Conclusion In hemophilia A plasma and whole blood, FXIII cotreatment with hemostatic agents accelerated FXIIIa formation, increased the generation and amount of fibrin α-chain crosslinked species, accelerated α2 -antiplasmin crosslinking, and increased clot weight. FXIII cotreatment with hemostatic therapy may augment hemostasis through increased crosslinking of fibrin and α2 -antiplasmin.

Finite element analysis of lordosis restoration with anterior longitudinal ligament release and lateral hyperlordotic cage placement.

PURPOSE: Restoring sagittal alignment is an important factor in the treatment of spinal deformities. Recent investigations have determined that releasing the anterior longitudinal ligament (ALL) and placing hyperlordotic cages can increase lordosis, while minimizing need for 3 column osteotomies. The influences of parameters such as cage height and angle have not been determined. Finite element analysis was employed to assess the extent of lordosis achievable after placement of different sized lordotic cages. METHODS: A 3-dimensional model of a L3-4 segment was used. Disc distraction was simulated by inserting interbody cages mid-body in the disc space. Analyses were performed in the following conditions: (1) intact, (2) ALL release, (3) ALL release + facetectomy, and (4) ALL release + posterior column osteotomy. Changes in segmental lordosis, disc height, foraminal height, and foraminal area were measured. RESULTS: After ALL resection and insertion of hyperlordotic cages, lordosis was increased in all cases. The lordosis achieved by the shorter cages was less due to posterior disc height maintained by the facet joints. A facetectomy increased segmental lordosis, but led to contact between the spinous processes. For some configurations, a posterior column osteotomy was required if the end goal was to match cage angle to intradiscal angle. CONCLUSION: Increased segmental lumbar lordosis is achievable with hyperlordotic cages after ALL resection. Increased cage height tended to increase the amount of lordosis achieved, although in some cases additional posterior bone resection was required to maximize lordosis. Further studies are needed to evaluate the impact on regional lumbar lordosis.

Effect of antioxidant vitamin supplementation on endothelial function in type 2 diabetes mellitus: a systematic review and meta-analysis of randomized controlled trials.

Controversy exists among trials assessing whether prolonged antioxidant vitamin supplementation improves endothelial function in type 2 diabetes mellitus (T2DM) subjects. The aim of this study was to systematically review and quantify the effect of antioxidant vitamin supplementation on endothelial function in T2DM subjects. MEDLINE, Cochrane, Scopus and Web of Science were searched up to February 2013 for randomized controlled trials assessing the effect of antioxidant vitamin E and/or C supplementation on endothelial function in T2DM subjects. Ten randomized controlled trials comparing antioxidant vitamin-supplemented and control groups (overall n = 296) met the inclusion criteria. Post-intervention standardized mean difference (SMD) in endothelial function did not reach statistical significance between groups (0.35; 95% confidence interval = -0.17, 0.88; P = 0.18). In subgroup analysis, post-intervention endothelial function was significantly improved by antioxidant vitamin supplementation in T2DM subgroups with body mass index (BMI) ≤ 29.45 kg m(-2) (SMD = 1.02; P < 0.05), but not in T2DM subgroups with BMI > 29.45 kg m(-2) (SMD = -0.07; P = 0.70). In meta-regression, an inverse association was found between BMI and post-intervention SMD in endothelial function (B = -0.024, P = 0.02). Prolonged antioxidant vitamin E and/or C supplementation could be effective to improve endothelial function in non-obese T2DM subjects.

Using the zygomatic root as a reference point in temporal lobe surgery.

BACKGROUND: The zygomatic root (ZR) is an anatomic landmark routinely identified during cranial procedures. Traditionally, it has been used for identification of structures other than temporal lobe anatomy. The aim of this study was to define the structural relationship between the ZR and temporal lobe anatomy and provide a consistent landmark to guide surgical dissection. To our knowledge, there have been no studies demonstrating this relationship. METHODS: Eighteen DICOM series were analyzed. 2 mm axial MRI slices were reconstructed with the x-axis centered along the zygoma. The posterior point of the ZR that marks the beginning of the groove between the zygoma and temporal bone was identified on all images. Several measures were taken to quantify the relationship of the zygomatic root to surgical landmarks used during temporal lobe surgery. RESULTS: The inferior temporal gyrus was always found just medial to the ZR. The mean distance between the ZR and temporal pole was 2.75 cm on the right and 2.78 cm on the left. The tip of the temporal horn was located on average 2.4 cm (left) and 2.31 cm (right) medial to the ZR. The tip of the temporal horn was found to be an average distance of 1 mm (left and right) posterior and 1.34 cm (left and right) superior to the ZR. All distances were measured orthogonally for each of the x, y, and z axes. CONCLUSION: The zygomatic root is an easily identifiable and consistent bony landmark that can serve as an adjuvant to neuronavigation for identification of temporal lobe surgical anatomy.

A Phase I dose-escalation study of the VEGFR inhibitor tivozanib hydrochloride with weekly paclitaxel in metastatic breast cancer.

Tivozanib is a potent selective tyrosine kinase inhibitor (TKI) of vascular endothelial growth factor receptors (VEGFRs) 1, 2, and 3. This Phase Ib study investigated the safety/tolerability, pharmacokinetics (PK), and activity of tivozanib with weekly paclitaxel in metastatic breast cancer (MBC). MBC patients with no prior VEGFR TKI treatment received daily oral tivozanib (3 weeks on, 1 week off) with weekly paclitaxel 90 mg/m(2). Standard 3 + 3 dose escalation was used; tivozanib cohorts (C) included C1 0.5 mg, C2 1.0 mg, and C3 1.5 mg. Assessments included Response Evaluation Criteria in Solid Tumors response, PK, and vascular function. Eighteen patients enrolled. Toxicities in >20 % of patients included fatigue, alopecia, nausea, diarrhea, peripheral sensory neuropathy, and hypertension. Grade 3/4 toxicities in >15 % of patients included fatigue and neutropenia. Maximum tolerated dose was tivozanib 1.5 mg with paclitaxel 90 mg/m(2). Four patients withdrew because of toxicity and one due to progressive disease. Thirteen patients were evaluable for response: four (30.8 %) had confirmed partial response; four had stable disease ≥6 months (30.8 %). PK data suggest no influence of paclitaxel on tivozanib concentrations. Tivozanib plus weekly paclitaxel was tolerable at all dose levels, supporting their combination at full dose. Activity in this small population was encouraging.

Phylogeography and environmental correlates of a cap on reproduction: teat number in a small marsupial, Antechinus agilis.

Natural selection should optimize litter size in response to the distribution and abundance of resources during breeding. In semelparous, litter-bearing antechinuses, teat number limits litter size. Consequently adaptation has been inferred in explaining intraspecific, geographic variability in teat number for several Antechinus spp. The phylogeography of teat number variation and associated genetic divergence were assessed in A. agilis using nine microsatellites and mitochondrial cytochrome b sequence data. Six-teat Otway Range animals were divergent in microsatellite allele identity and frequencies: samples from three Otway six-teat sites demonstrated significantly greater similarity genetically to those from six-teat animals approximately 250 km to the west, than to nearby Otway 10-teat samples, or to the six-teat animals at Wilsons Promontory. Gene flow between Otway phenotypes appears to have been limited for sufficient time to enable different microsatellite alleles to evolve. Nonetheless, nuclear genetic evidence suggested only incomplete reproductive isolation, and mitochondrial DNA (mtDNA) haplotypes showed no association with teat number. Other populations across the range were no more genetically differentiated from one another than expected from geographic separation. Principal components and distance-based redundancy analyses found an association between environmental variables and geographic distribution of A. agilis teat number - six-teat animals inhabit more temperate forests, whilst those with more teats experience greater seasonality. The apparent restricted breeding between phenotypically distinct animals, together with phylogenetically separate groups of six-teat animals in different locations with similar environments, are consistent with the hypothesis that adaptation to different habitats drives teat number variation in A. agilis.

Reduction in IV t-PA door to needle times using an Acute Stroke Triage Pathway.

OBJECTIVE: To determine the effectiveness of an Acute Stroke Triage Pathway in reducing door to needle times in acute stroke treatment with IV t-PA. BACKGROUND: A previous study at our tertiary referral centre, examining IV t-PA door to needle times, was completed in 2000. The median door to needle time was beyond the recommended National Institute for Neurological Disorders and Stroke (NINDS) standard of 60 minutes. In November 2001, an Acute Stroke Triage Pathway was introduced in the emergency room (ER) to address this issue. The goal of this pathway was to rapidly identify patients eligible for treatment for IV t-PA, so that CT scans and lab studies could be arranged immediately upon ER arrival. Our hypothesis was that the Triage Pathway would shorten door to CT and door to needle times. DESIGN/METHODS: Using retrospective data, pre (n=87) and post (n=47) triage pathway times were compared. The door to CT time was reduced by 11 minutes (p=0.015) and door to needle time was reduced by 18 minutes (p=0.0036) in a subgroup of patients that presented directly to our hospital. CONCLUSIONS: These results indicate that the Acute Stroke Triage Pathway is effective in reducing Door to CT and Door to Needle Times in patients presenting directly to our ER. However, a majority of treatment times were still beyond NINDS recommendations. Stroke Centers require periodic review of their efficiency to ensure that target times are being obtained and may benefit from the use of an Acute Stroke Triage Pathway.

The role of total and high-molecular-weight complex of adiponectin in vascular function in offspring whose parents both had type 2 diabetes.

AIMS/HYPOTHESIS: Adiponectin is an adipokine with insulin-sensitising and anti-atherogenic properties. We studied the role played by total adiponectin and by the bioactive high-molecular-weight (HMW) oligomeric complexes of adiponectin in vascular function in offspring whose parents both had type 2 diabetes, a population at high risk of diabetes and atherosclerosis. METHODS: Total and %HMW adiponectin, the cytokines C-reactive protein, interleukin-6 and plasminogen activator inhibitor-1 (PAI-1), as well as lipid profiles were assayed in 19 offspring, each with two type 2 diabetic parents. Subjects underwent OGTTs and IVGTTs. Endothelium-dependent vasodilation (EDV) was assessed by brachial artery ultrasonography. RESULTS: There was a significant relationship between %HMW and total adiponectin levels (r=0.72, p=0.001). Despite an expected strong positive correlation between HDL-cholesterol and adiponectin levels (r=0.52, p=0.04), as well as HDL-cholesterol and EDV (r=0.56, p<0.02), there was no significant relationship between either total adiponectin or % HMW adiponectin and EDV. Adiponectin was inversely associated with PAI-1 (r=0.50, p=0.05), but did not correlate with the inflammatory markers C-reactive protein or interleukin-6. CONCLUSIONS/INTERPRETATION: In offspring of diabetic parents, a population at high risk of diabetes and atherosclerotic disease, there is no relationship between total or %HMW adiponectin and endothelium-dependent vasodilation. However, low adiponectin was associated with impaired fibrinolysis as manifested by increased levels of plasminogen activator inhibitor-1.

Ictal asystole with convulsive syncope mimicking secondary generalisation: a depth electrode study.

Ictal bradycardia is rare and its localising value is debated. Bradyarrhythmias are, however, important because of their potential connection to sudden death and ability to affect clinical seizure manifestations. Cerebral hypoperfusion induces loss of consciousness, at times with myoclonic jerks, whose clinical differentiation from a generalised convulsive seizure may prove difficult. Two invasive and five surface monitored seizures recorded over two years in a 51 year old woman with post-traumatic epilepsy characterised by seizure-triggered asystole were analysed. All seven seizures showed left temporal onset. Both intracranially recorded events started in the left anterior hippocampus/amygdala, spreading to the contralateral hippocampus in 35 and 25 seconds. Within 10 seconds an electrocardiogram showed asystole lasting 21 and 28 seconds, associated with suppression of recorded cerebral electrical activity, except a polyspike suppression pattern remaining in the hippocampi. Clinically, the patient, concomitantly with the cerebral suppression, developed myoclonic twitches of the limbs. A dual chamber cardiac pacemaker was implanted; at 11 months follow up, the patient has experienced only infrequent partial seizures, with none involving falls or shaking. Left temporal lobe seizures produced convulsive syncope initiated by ictal asystole. These observations suggest that intertemporal spread is necessary, though not sufficient, to produce bradycardia and asystole. Furthermore, pacemakers may decrease seizure severity, as well as potentially protect against malignant bradyarrhythmias.

Nutrient digestibility of diets with different fiber to starch ratios when fed to lactating dairy cows.

The objective of this experiment was to determine whether increasing the dietary neutral detergent fiber (NDF):starch ratio affected NDF digestibility when diets were formulated to have equal in situ NDF digestibility. Six lactating Holstein cows were fed 1 of 3 diets in a replicated 3 x 3 Latin square. All diets had 41.5% of the dry matter (DM) as corn silage but the concentration of corn grain varied from 23.3 to 34.8% and the NDF:starch ratios were 0.74, 0.95, and 1.27. As corn grain increased, the concentration of a mixture of 54% soyhulls and 46% cottonseed hulls decreased. The soyhull:cottonseed hull mixture had the same in situ NDF digestibility as the corn silage. All diets had 18% forage NDF but starch concentration varied from 25.4 to 33.3% and NDF varied from 24.7 to 32.2%. Intake tended to increase as the NDF:starch ratio increased. Total tract digestibility (measured by total collection of feces and urine) of dry matter and energy decreased linearly as the NDF:starch ratio increased, but NDF digestibility was not affected by treatment. Retention of N increased linearly as the NDF:starch ratio increased. As dietary NDF:starch ratio increased, ruminal pH was not affected, but the concentration of total volatile fatty acids (VFA) decreased and the VFA profile was altered by diet. Consistent with the observed changes in ruminal VFA, milk fat percentage increased with increasing dietary NDF:starch. Intake of digestible energy and output of energy in milk and body weight change was not affected by treatment.

The impact of metal catalysis on protein tyrosine nitration by peroxynitrite.

In a series of heme and non-heme proteins the nitration of tyrosine residues was assessed by complete pronase digestion and subsequent HPLC-based separation of 3-nitrotyrosine. Bolus addition of peroxynitrite caused comparable nitration levels in all tested proteins. Nitration mainly depended on the total amount of tyrosine residues as well as on surface exposition. In contrast, when superoxide and nitrogen monoxide (NO) were generated at equal rates to yield low steady-state concentrations of peroxynitrite, metal catalysis seemed to play a dominant role in determining the sensitivity and selectivity of peroxynitrite-mediated tyrosine nitration in proteins. Especially, the heme-thiolate containing proteins cytochrome P450(BM-3) (wild type and F87Y variant) and prostacyclin synthase were nitrated with high efficacy. Nitration by co-generated NO/O(2)(-) was inhibited in the presence of superoxide dismutase. The NO source alone only yielded background nitration levels. Upon changing the NO/O(2)(-) ratio to an excess of NO, a decrease in nitration in agreement with trapping of peroxynitrite and derived radicals by NO was observed. These results clearly identify peroxynitrite as the nitrating species even at low steady-state concentrations and demonstrate that metal catalysis plays an important role in nitration of protein-bound tyrosine.

Fluorescence assay for monitoring Zn-deficient superoxide dismutase in vitro.

A method has been developed for selective detection of the zinc-deficient form of Cu, Zn superoxide dismutase (SOD1) in vitro. Zinc-deficient SOD1 mutants have been implicated in the death of motor neurons leading in amyotrophic lateral sclerosis (ALS or Lou Gerhig's disease). Thus, this method may have applicability for detecting zinc-deficient SOD1 mutants in human ALS patients samples as well as in a transgenic mouse model of ALS and in cultured motor neurons. We determined previously that structural analogs of 1,10 phenanthroline, which react specifically with Cu(I), react with the active Cu(I) of SOD1 when zinc is absent, but not when zinc is also bound, as evidenced by the fact that the reaction is inhibited by pretreatment of the enzyme with zinc. We report herein that bathocuproine, or its water-soluble derivative bathocuproine disulfonate, react with zinc-deficient SOD1 to form a complex which fluoresces at 734 nm when excited at 482 nm. Fluorescent intensity is concentration dependent, thus we propose to use fluorescent confocal microscopy to measure intracellular levels of zinc-deficient SOD1 in situ.

Radiation therapy impairs endothelium-dependent vasodilation in humans.

OBJECTIVES: The objective of this study was to test the hypothesis that external-beam radiation induces a chronic impairment of endothelium-dependent vasodilation. BACKGROUND: Radiation therapy is used commonly in the treatment of cancer and is associated with an increased incidence of adverse vascular events related to the field of radiation, including stroke and myocardial infarction. As endothelial injury is central to the pathogenesis of vascular diseases, we hypothesized that radiotherapy induces arterial endothelial dysfunction. METHODS: Sixteen women with unilateral breast cancer who underwent standard external-beam radiation therapy to the breast and axilla >3 years before enrollment and ten healthy women were studied. Vascular ultrasonography was used to image both the artery exposed to radiation and the contralateral artery. Flow-mediated, endothelium-dependent vasodilation and endothelium-independent vasodilation to nitroglycerin of both axillary arteries were measured. RESULTS: Endothelium-dependent vasodilation was significantly impaired in the irradiated axillary arteries compared with the contralateral, nonirradiated arteries (-0.4 +/- 0.4% vs. 3.2 +/- 0.8% p < 0.001) and also compared with control subjects' arteries (-0.4 +/- 0.4% vs. 2.5 +/- 0.6%, p < 0.001). In contrast, endothelium-independent vasodilation was greater in the arteries that received radiation compared with the contralateral arteries (3.8 +/- 0.5% vs. 2.0 +/- 0.4%, p < 0.05) and also compared with control arteries (3.8 +/- 0.5% vs. 2.5 +/- 0.4%, p < 0.05). CONCLUSIONS: External beam radiation therapy impairs endothelium-dependent vasodilation of conduit arteries, implicating a decrease in the bioavailability of nitric oxide. These abnormalities may contribute to the development of arterial occlusive disease and associated clinical events.

Relationship of clinical presentation and calcification of culprit coronary artery stenoses.

Coronary artery calcification is increased in the presence of atherosclerosis. However, there is great variability in the calcification of individual coronary stenoses, and the clinical significance of this finding remains unknown. We tested the hypothesis that culprit lesions associated with myocardial infarction or unstable angina are less calcified than are stenoses associated with stable angina. The study consisted of 78 patients who underwent intravascular ultrasound imaging of culprit stenoses after the placement of a stent. Seventeen patients presented with stable angina; 43, with unstable angina; and 18, with myocardial infarction. The extent of coronary calcification was measured by the angle of its arc and was quantified with a computer-based protractor. The arc of calcium was measured in the stented area at the point of maximal calcification and also as an average of the calcification found at proximal, middle, and distal stent segments. The maximal arc of calcium decreased progressively from patients with stable angina (91+/-10 degrees ) to those with unstable angina (59+/-8 degrees ) and to those with myocardial infarction (49+/-11 degrees, P=0.014). Similarly, the average arc of calcium was greatest (32+/-7 degrees ) in patients with stable angina, less (15+/-4 degrees ) in patients with unstable angina, and least (10+/-5 degrees ) in patients with acute myocardial infarction (P=0.014). These associations remained significant after adjustment for other factors that potentially affect arterial calcification. Acute coronary syndromes are associated with a relative lack of calcium in the culprit stenoses compared with stenoses of patients with stable angina. These findings have implications for the understanding of the biology of acute coronary syndromes as well as for the identification of coronary stenoses by methods that rely solely on the presence of calcium.

Functional conservation between the human, nematode, and yeast CK2 cell cycle genes.

Protein kinase CK2 (formerly casein kinase II) is a highly conserved serine/threonine protein kinase ubiquitous in eukaryotic organisms. Previously, we have shown that CK2 is required for cell cycle progression and essential for the viability of the yeast Saccharomyces cerevisiae. We now report that either the human or the nematode Caenorhabditis elegans CK2alpha catalytic subunit can substitute for the yeast catalytic subunits. Additionally, expression of the human CK2 regulatory subunit (CK2beta) can suppress the temperature sensitivity of either of the two yeast CK2 mutant catalytic subunits. Taken together, these observations reinforce the view that the CK2 cell cycle progression genes have been highly conserved during evolution from yeast to humans, not only in structure but also in function.

Bms1p, a novel GTP-binding protein, and the related Tsr1p are required for distinct steps of 40S ribosome biogenesis in yeast.

Bms1p and Tsr1p define a novel family of proteins required for synthesis of 40S ribosomal subunits in Saccharomyces cerevisiae. Both are essential and localize to the nucleolus. Tsr1p shares two extended regions of similarity with Bms1p, but the two proteins function at different steps in 40S ribosome maturation. Inactivation of Bms1p blocks at an early step, leading to disappearance of 20S and 18S rRNA precursors. Also, slight accumulation of an aberrant 23S product and significant 35S accumulation are observed, indicating that pre-rRNA processing at sites A0, A1, and A2 is inhibited. In contrast, depletion of Tsr1p results in accumulation of 20S rRNA. Because processing of 20S to 18S rRNA occurs in the cytoplasm, this suggests that Tsr1p is required for assembly of a transport- or maturation-competent particle or is specifically required for transport of 43S pre-ribosomal particles, but not 60S ribosome precursors, from the nucleus to the cytosol. Finally, Bms1p is a GTP-binding protein, the first found to function in ribosome assembly or rRNA processing.