The Saccharomyces cerevisiae spindle pole body duplication gene MPS1 is part of a mitotic checkpoint

M-phase checkpoints inhibit cell division when mitotic spindle function is perturbed. Here we show that the Saccharomyces cerevisiae MPS1 gene product, an essential protein kinase required for spindle pole body (SPB) duplication (Winey et al., 1991; Lauze et al., 1995), is also required for M-phase check-point function. In cdc31-2 and mps2-1 mutants, conditional failure of SPB duplication results in cell cycle arrest with high p34CDC28 kinase activity that depends on the presence of the wild-type MAD1 checkpoint gene, consistent with checkpoint arrest of mitosis. In contrast, mps1 mutant cells fail to duplicate their SPBs and do not arrest division at 37 degrees C, exhibiting a normal cycle of p34CDC28 kinase activity despite the presence of a monopolar spindle. Double mutant cdc31-2, mps1-1 cells also fail to arrest mitosis at 37 degrees C, despite having SPB structures similar to cdc31-2 single mutants as determined by EM analysis. Arrest of mitosis upon microtubule depolymerization by nocodazole is also conditionally absent in mps1 strains. This is observed in mps1 cells synchronized in S phase with hydroxyurea before exposure to nocodazole, indicating that failure of checkpoint function in mps1 cells is independent of SPB duplication failure. In contrast, hydroxyurea arrest and a number of other cdc mutant arrest phenotypes are unaffected by mps1 alleles. We propose that the essential MPS1 protein kinase functions both in SPB duplication and in a mitotic checkpoint monitoring spindle integrity.

Pathophysiologic basis of contrast enhancement in breast tumors

While the diagnostic benefits of gadolinium (Gd)-chelate contrast agents are firmly established in magnetic resonance imaging (MRI) of tumors, the pathophysiologic basis of the enhancement observed and its histopathologic correlate remained vague. Tumor angiogenesis is fundamental for growth and metastasis and also of interest in new therapeutic concepts. By correlative analysis of a) histology; b) vascular density (CD31); and c) vascular permeability (vascular permeability factor/vascular endothelial growth factor [VPF/VEGF]), we found a) significantly (P < 0.001) faster exchange rates in malignant compared with benign breast lesions; b) distinct differences in enhancement characteristics between the histologic types (invasive ductal carcinoma, invasive lobular carcinoma, and ductal carcinoma in situ); and c) dependence of enhancement kinetics on the VPF/VEGF expression. The pathophysiologic basis for the differences in contrast enhancement patterns of tumors detectable by MRI is mainly due to vascular permeability, which leads to more characteristic differences than vascular density. MRI is able to subclassify malignant breast tumors due to their different angiogenetic properties.

Activation of the budding yeast spindle assembly checkpoint without mitotic spindle disruption

The spindle assembly checkpoint keeps cells with defective spindles from initiating chromosome segregation. The protein kinase Mps1 phosphorylates the yeast protein Mad1p when this checkpoint is activated, and the overexpression of Mps1p induces modification of Mad1p and arrests wild-type yeast cells in mitosis with morphologically normal spindles. Spindle assembly checkpoint mutants overexpressing Mps1p pass through mitosis without delay and can produce viable progeny, which demonstrates that the arrest of wild-type cells results from inappropriate activation of the checkpoint in cells whose spindle is fully functional. Ectopic activation of cell-cycle checkpoints might be used to exploit the differences in checkpoint status between normal and tumor cells and thus improve the selectivity of chemotherapy.

Phylogenetic diversity of the Rickettsiae

Small subunit rRNA sequences have been determined for representative strains of six species of the family Rickettsiaceae: Rickettsia rickettsii, Rickettsia prowazekii, Rickettsia typhi, Coxiella burnetii, Ehrlichia risticii, and Wolbachia persica. The relationships among these sequences and those of other eubacteria show that all members of the family Rickettsiaceae belong to the so-called purple bacterial phylum. The three representatives of the genus Rickettsia form a tight monophyletic cluster within the alpha subdivision of the purple bacteria. E. risticii also belongs to the alpha subdivision and shows a distant yet specific relationship to the genus Rickettsia. However, the family as a whole is not monophyletic, in that C. burnetii and W. persica are members of the gamma subdivision. The former appears to show a specific, but rather distant, relationship to the genus Legionella.

The influence of verapamil on serum digoxin concentration

The effect of verapamil on the pharmacokinetics of digoxin was studied in 49 patients with chronic atrial fibrillation. A dose of 240 mg/day of verapamil was given to the patients who were receiving a stable dose of digoxin. Serum digoxin levels rose from 0.76 +/- 0.54 ng/ml (mean +/- SD) to 1.31 +/- 0.54 ng/ml during verapamil treatment (p less than 0.0005). This effect was dose-dependent, as shown in seven subjects who received 160 mg and then, 240 mg of verapamil: There was a stepwise rise in serum digoxin concentration from a control value of 0.60 +/- 0.11 ng/ml to 0.84 +/- 0.18 ng/ml and 1.24 +/- 0.40 ng/ml, respectively (p less than 0.01 for both steps). The effect of verapamil developed gradually within the first few days in seven subjects in whom serum digoxin concentration reached, within 7 days, 90% of the increase observed 14 days after onset of verapamil. Renal digoxin clearance decreased significantly (26.1 +/- 0.7 vs 55.1 +/- 12.3 ml/min, p less than 0.005) in six patients in whom serum digoxin concentration increased. It did not change in one patient in whom serum digoxin concentration was not influenced by verapamil. Creatine clearance did not change in any of these seven. The same effects on digoxin clearance were observed in three normal subjects. Among the 49 patients, verapamil resulted in the development of signs and symptoms that suggested digitalis toxicity in seven. Verapamil significantly increased serum digoxin concentration. The process is dose-dependent and gradual, and it is at least partially explained by reduced renal excretion without reduction in glomerular filtration. The dose of digoxin may need readjustment in patients who are concomitantly receiving verapamil.

The DNA sequence of the H-2kb gene: evidence for gene conversion as a mechanism for the generation of polymorphism in histocompatibilty antigens

We have determined the DNA sequence of the H-2Kb gene of the C57B1/10 mouse. Comparison of this sequence with that of the allelic H-2Kd shows surprisingly that the exons have accumulated more mutations than their introns. Moreover, many of these changes in the exons are clustered in short regions or hot spots. Additional comparison of these sequences with the H-2Ld and H-2Db sequences shows that, in several cases, the altered sequence generated at the hot spot is identical to the corresponding region of a non-allelic H-2 gene. The clustered changes are responsible for 60% of the amino acid differences between the H-2Kb and H-2Kd genes and suggest that micro-gene conversion events occurring within the exons and involving only tens of nucleotides are an important mechanism for the generation of polymorphic differences between natural H-2 alleles.

How thick is too thick? When endometrial thickness should prompt biopsy in postmenopausal women without vaginal bleeding

OBJECTIVE

Transvaginal sonography (TVS) is routinely performed as part of a pelvic sonogram in postmenopausal women, and images of the endometrium are frequently obtained. In women without vaginal bleeding, the threshold separating normal from abnormally thickened endometrium is not known. The aim of this study was to determine an endometrial thickness threshold that should prompt biopsy in a postmenopausal woman without vaginal bleeding.

METHODS

This was a theoretical cohort of postmenopausal women aged 50 years and older who were not receiving hormone therapy. We determined the risk of cancer for a postmenopausal woman with vaginal bleeding when the endometrial thickness measures > 5 mm, and then determined the endometrial thickness in a woman without vaginal bleeding that would be associated with the same risk of cancer. We used published and unpublished data to determine the sensitivity and specificity of TVS, the incidence of endometrial cancer, the percentage of women symptomatic with vaginal bleeding, and the percentage of cancer that occurs in women without vaginal bleeding. Ranges for each estimate were included in a sensitivity analysis to determine the impact of each estimate on the overall results.

RESULTS

In a postmenopausal woman with vaginal bleeding, the risk of cancer is approximately 7.3% if her endometrium is thick (> 5 mm) and < 0.07% if her endometrium is thin (< or = 5 mm). An 11-mm threshold yields a similar separation between those who are at high risk and those who are at low risk for endometrial cancer. In postmenopausal women without vaginal bleeding, the risk of cancer is approximately 6.7% if the endometrium is thick (> 11 mm) and 0.002% if the endometrium is thin (< or = 11 mm). The estimated risk of cancer was sensitive to the percentage of cancer cases that were estimated to occur in women without vaginal bleeding. For the base case we estimated that 15% of cancers occur in women without vaginal bleeding. When we changed the estimate to project that only 5% of cancers occur in women without vaginal bleeding, the projected risk of cancer with a thick measurement was only 2.2%, whereas when we estimated that 20% of endometrial cancers occur in women without bleeding, the projected risk of cancer with a thick measurement was 8.9%. As a woman's age increases, her risk of cancer increases at each endometrial thickness measurement. For example, using the 11 mm threshold, the risk of cancer associated with a thick endometrium increases from 4.1% at age 50 years to 9.3% at age 79 years. Varying the other estimates used in the decision analysis within plausible ranges had no substantial effect on the results.

CONCLUSIONS

In a postmenopausal woman without vaginal bleeding, if the endometrium measures > 11 mm a biopsy should be considered as the risk of cancer is 6.7%, whereas if the endometrium measures < or = 11 mm a biopsy is not needed as the risk of cancer is extremely low.

Detection of soluble HLA-G molecules in plasma and amniotic fluid

Although the cDNA sequence of HLA-G antigens is compatible with their expression as soluble molecules (sHLA-G), the determination of native sHLA-G levels in body fluids has not yet been described. The lack of this information is likely to reflect the difficulties in developing an assay suitable to measure sHLA-G antigens in the presence of soluble HLA-A, -B and -C (sHLA-I) antigens, since most of the available anti-HLA-G mAb do not detect soluble beta2-m associated HLA-G antigens or crossreact with sHLA-I antigens. Therefore, we have developed a two-step assay which eliminates the interference of classical HLA class I antigens. In the first step, the sample is depleted of sHLA-I antigens and of HLA-E antigens with mAb TP25.99. Then, HLA-G antigens are captured with mAb W6/32 and detected with anti-beta2-m mAb in ELISA. Utilizing this assay, sHLA-G antigen levels were measured in EDTA plasma from 92 controls with known HLA types, 28 women at delivery and the corresponding cord bloods and in 50 amniotic fluids. Mean sHLA-G plasma levels did not differ between males (24.9+/-3.0 SEM ng/ml; n=42) and females (20.1+/-2.1 SEM ng/ml; n = 50). However, sHLA-G levels in HLA-A11 positive probands (mean: 13.0+/-4.4 SEM ng/ml; n=12) were significantly (P<0.05) lower than in HLA-A11 negative ones (mean: 24.5+/-2.0 SEM ng/ml; n=80). sHLA-G levels in women at delivery (mean: 22.9+/-2.2 SEM ng/ml; n=28) were in the range of controls but were significantly (P<0.001) reduced in the corresponding cord bloods (mean: 13.8+/-1.5 SEM ng/ml; n=28). sHLA-G levels in amniotic fluids (mean: 15.5 + 1.0 SEM ng/ml; n=50) were significantly (P<0.001) lower than in plasma. sHLA-G levels were 5 and 11% of those of sHLA-I antigens in plasmas and amniotic fluids, respectively. Individual sHLA-G levels were not correlated with sHLA-I levels. SDS-PAGE analysis of plasma sHLA-G antigens revealed two molecular variants with a 35 kD and a 27 kD MW corresponding to the sizes of sHLA-G1 and -G2 isoforms. In conclusion, our study has shown that the two-step assay we have developed is reliable in measuring sHLA-G antigen levels. This assay will facilitate the analysis of the biological and clinical significance of sHLA-G antigens in plasma.

Sex differences in brain activation pattern during a visuospatial cognitive task: a functional magnetic resonance imaging study in healthy volunteers

Sex differences in mental rotation tasks, favoring men, have been noted in behavioral studies and functional imaging studies. In the present study ten female and ten male volunteers underwent functional magnetic resonance imaging in a conventional block design. Regions of activation were detected after performance of a mental rotation task inside the scanner. In contrast to previous studies, confounding factors such as performance differences between genders or high error rates were excluded. Men showed significantly stronger parietal activation, while women showed significantly greater right frontal activation. Our results point to gender specific differences in the neuropsychological processes involved in mental rotation tasks.

Determination of kinetic constants for the interaction between a monoclonal antibody and peptides using surface plasmon resonance

Differences in the affinity of a monoclonal antibody raised against the protein of tobacco mosaic virus for 15 related peptides (residues 134-146) carrying single-residue modifications were investigated using a novel biosensor technology (Pharmacia BIAcore). Analysis of the peptide-antibody interaction in real time allowed fast and reproducible measurements of both association and dissociation rate constants. Out of 15 mutant peptides analyzed, five were not recognized by the antibody at all, and seven were recognized as well as the wild-type peptide. For three of the peptides, the rate constants were different for the mutant and wild-type peptides. The pattern of residue recognition suggests that the epitope is formed by three residues (140, 143, and 144) in a helical conformation that mimics the structure in the protein. Even a minor modification of these residues totally abolishes recognition by the antibody. Modifications of adjacent residues result in small but significant differences in association and/or dissociation rate constants. One of the recognized residues is totally buried in the three-dimensional structure of TMV protein, suggesting that a structural rearrangement next to the helix occurs during protein-antibody interaction.

Yeast spindle pole body duplication gene MPS1 encodes an essential dual specificity protein kinase

The MPS1 gene has been previously identified by a mutant allele that shows defects in spindle pole body (SPB) duplication and cell cycle control. The SPB is the centrosome-equivalent organelle in the yeast Saccharomyces cerevisiae, and it nucleates all the microtubules in the cell. We report the isolation of the MPS1 gene, which encodes an essential protein kinase homolog. The MPS1 open reading frame has been fused to those that encode the LexA protein or the GST protein and both of these constructs function in yeast. The fusion proteins have been affinity-purified from yeast extracts and the GST chimeric protein has been found to be a phosphoprotein. Both proteins have been used to demonstrate intrinsic in vitro protein kinase activity of Mps1p against exogenous substrates and itself (autophosphorylation). A mutation predicted to abolish kinase function not only eliminates in vitro protein kinase activity, but also behaves like a null mutation in vivo, suggesting that kinase activity contributes to the essential function of the protein. Phosphoamino acid analysis of substrates phosphorylated by Mps1p indicates that this kinase can phosphorylate serine, threonine and tyrosine residues, identifying Mps1p as a dual specificity protein kinase.

Association of olanzapine-induced weight gain with an increase in body fat

OBJECTIVE

The goal of this study was to explore the pathophysiology of weight gain during treatment with olanzapine for schizophrenia.

METHOD

The authors used a prospective, controlled, open study comparing body weight, body mass index, and related biological measures in mentally and physically healthy volunteers and olanzapine-treated patients with schizophrenia. Weight, eating behavior, leptin serum levels, body mass index, and body composition were assessed over an 8-week observation period.

RESULTS

A significant increase in body weight, leptin serum levels, and percentage of body fat was seen in patients treated with olanzapine, but the drug-free comparison group did not show any significant changes. The weight gain during antipsychotic treatment with olanzapine was mainly attributable to an increase in body fat; patients' lean body mass did not change.

CONCLUSIONS

In addition to the original finding that an increase in body fat is mainly responsible for olanzapine-induced weight gain, these findings confirm results obtained in other studies showing increases in body weight and serum leptin levels during treatment with second-generation antipsychotics.

Separation of viable Rickettsia typhi from yolk sac and L cell host components by renografin density gradient centrifugation

Rickettsia typhi cultivated in the yolk sac of chicken embryos or in L cells irradiated 7 days previously was separated from host cell components by two cycles of Renografin density gradient centrifugation. Preliminary steps involved differential centrifugation and centrifugation over a layer of 10% bovine plasma albumin of infected yolk sac suspensions, or trypsinization and passage through filters of wide porosity of infected L cell suspensions. Rickettsial preparations obtained by these methods appeared to be free from host cell components while retaining high levels of hemolytic activity, egg infectivity, and capacity to catabolize glutamate. Average yields were 3.3 mg of rickettsial protein per yolk sac or 0.44 mg per 16-oz (ca. 475-ml) L cell culture. Extracts from these two preparations displayed malate dehydrogenase activity of electrophoretic mobility identical to each other but quite different in migration patterns from the corresponding host cell enzymes. This method of separation of rickettsiae from host cell constituents appears to be particularly well suited for the study of rickettsial enzymatic activity.

Efficacy and safety of sodium phosphate tablets compared with PEG solution in colon cleansing: two identically designed, randomized, controlled, parallel group, multicenter phase III trials

BACKGROUND

Liquid purgatives for cleansing before colonoscopy often are poorly tolerated. A sodium phosphate tablet has been developed to provide equivalent efficacy with better patient tolerance. These 2 studies compare the safety, efficacy, and patient acceptance of the tablet (Visicol) to a polyethylene glycol (PEG) solution in adults undergoing colonoscopy.

METHODS

Two identically designed, randomized, investigator-blinded, multicenter trials were performed. The primary efficacy variable was the overall quality of colon cleansing. Patient tolerance was assessed in terms of compliance with the dosing regimen. Safety assessments included recording of adverse events and changes in biochemical tests, electrocardiogram, and vital signs.

RESULTS

Eight hundred forty-five patients participated in the studies; 420 took sodium phosphate tablets and 425 took a PEG solution. The 2 methods of preparation were equivalent in the overall quality of colon cleansing, cleansing in the right colon, and the frequency of inadequate preparation. Overall cleansing was excellent or good in 84.3% of patients in the tablet group and in 76.7% in the PEG group. Patient compliance was greater in the tablet group. There were also significantly fewer GI side effects in this group.

CONCLUSIONS

Sodium phosphate tablets, compared with PEG solution, produce equivalent colon cleansing, are associated with fewer GI side effects, and are better tolerated by patients.

Survival after neoadjuvant chemotherapy with or without bevacizumab or everolimus for HER2-negative primary breast cancer (GBG 44-GeparQuinto)†

BACKGROUND

The GeparQuinto study showed that adding bevacizumab to 24 weeks of anthracycline-taxane-based neoadjuvant chemotherapy increases pathological complete response (pCR) rates overall and specifically in patients with triple-negative breast cancer (TNBC). No difference in pCR rate was observed for adding everolimus to paclitaxel in nonearly responding patients. Here, we present disease-free (DFS) and overall survival (OS) analyses.

PATIENTS AND METHODS

Patients (n = 1948) with HER2-negative tumors of a median tumor size of 4 cm were randomly assigned to neoadjuvant treatment with epirubicin/cyclophosphamide followed by docetaxel (EC-T) with or without eight infusions of bevacizumab every 3 weeks before surgery. Patients without clinical response to EC ± Bevacizumab were randomized to 12 weekly cycles paclitaxel with or without everolimus 5 mg/day. To detect a hazard ratio (HR) of 0.75 (α = 0.05, β = 0.8) 379 events had to be observed in the bevacizumab arms.

RESULTS

With a median follow-up of 3.8 years, 3-year DFS was 80.8% and 3-year OS was 89.7%. Outcome was not different for patients receiving bevacizumab (HR 1.03; P = 0.784 for DFS and HR 0.974; P = 0.842 for OS) compared with patients receiving chemotherapy alone. Patients with TNBC similarly showed no improvement in DFS (HR = 0.99; P = 0.941) and OS (HR = 1.02; P = 0.891) when treated with bevacizumab. No other predefined subgroup (HR+/HER2-; locally advanced (cT4 or cN3) or not; cT1-3 or cT4; pCR or not) showed a significant benefit. No difference in DFS (HR 0.997; P = 0.987) and OS (HR 1.11; P = 0.658) was observed for nonearly responding patients receiving paclitaxel with or without everolimus overall as well as in subgroups.

CONCLUSIONS

Long-term results, in opposite to the results of pCR, do not support the neoadjuvant use of bevacizumab in addition to an anthracycline-taxane-based chemotherapy or everolimus in addition to paclitaxel for nonearly responding patients.

CLINICAL TRIAL NUMBER

NCT 00567554, www.clinicaltrials.gov.

Stapled haemorrhoidopexy: a consensus position paper by an international working party - indications, contra-indications and technique

An international working party with experience in the performance of an alternative haemorrhoid operation through the use of the circular stapler was convened for the purpose of developing a consensus as to the criteria for undertaking this procedure. The agenda consisted of first, naming the operation; second, the indications and contra-indications for its performance; and third, the preferred surgical technique. Among the recommendations for individuals who plan to embark on this surgery are that experience with anorectal surgery and an understanding of anorectal anatomy are requisites; experience with circular stapling devices is essential; and the surgeon must attend a formal course which should include lectures, videos, the application of the instrument in models, and observation of the operation as performed by a surgeon recognized by his or her peers-leading ultimately to undertaking the procedure while being observed by an experienced surgeon. Following satisfactory completion of the above, independent responsibility should be determined by an individual's department of surgery.

Neutrophil gelatinase-associated lipocalin is a biomarker of acute-on-chronic liver failure and prognosis in cirrhosis

BACKGROUND & AIMS

Acute-on-chronic liver failure (ACLF) is a syndrome that occurs in cirrhosis characterized by organ failure(s) and high mortality rate. There are no biomarkers of ACLF. The LCN2 gene and its product, neutrophil gelatinase-associated lipocalin (NGAL), are upregulated in experimental models of liver injury and cultured hepatocytes as a result of injury by toxins or proinflammatory cytokines, particularly Interleukin-6. The aim of this study was to investigate whether NGAL could be a biomarker of ACLF and whether LCN2 gene may be upregulated in the liver in ACLF.

METHODS

We analyzed urine and plasma NGAL levels in 716 patients hospitalized for complications of cirrhosis, 148 with ACLF. LCN2 expression was assessed in liver biopsies from 29 additional patients with decompensated cirrhosis with and without ACLF.

RESULTS

Urine NGAL was markedly increased in ACLF vs. no ACLF patients (108(35-400) vs. 29(12-73)μg/g creatinine; p<0.001) and was an independent predictive factor of ACLF; the independent association persisted after adjustment for kidney function or exclusion of variables present in ACLF definition. Urine NGAL was also an independent predictive factor of 28day transplant-free mortality together with MELD score and leukocyte count (AUROC 0.88(0.83-0.92)). Urine NGAL improved significantly the accuracy of MELD in predicting prognosis. The LCN2 gene was markedly upregulated in the liver of patients with ACLF. Gene expression correlated directly with serum bilirubin and INR (r=0.79; p<0.001 and r=0.67; p<0.001), MELD (r=0.68; p<0.001) and Interleukin-6 (r=0.65; p<0.001).

CONCLUSIONS

NGAL is a biomarker of ACLF and prognosis and correlates with liver failure and systemic inflammation. There is remarkable overexpression of LCN2 gene in the liver in ACLF syndrome.

LAY SUMMARY

Urine NGAL is a biomarker of acute-on-chronic liver failure (ACLF). NGAL is a protein that may be expressed in several tissues in response to injury. The protein is filtered by the kidneys due to its small size and can be measured in the urine. Ariza, Graupera and colleagues found in a series of 716 patients with cirrhosis that urine NGAL was markedly increased in patients with ACLF and correlated with prognosis. Moreover, gene coding NGAL was markedly overexpressed in the liver tissue in ACLF.

Expression of murine H-2Kb histocompatibility antigen in cells transformed with cloned H-2 genes

Cosmids containing H-2 histocompatibility antigen genes of the H-2b haplotype have been isolated. One of these genes expresses a 45,000 molecular weight protein, indistinguishable from H-2Kb when introduced into mouse L cells. These H-2Kb transformed L cells can be killed by allospecific anti-H-2Kb cytotoxic T cells. Moreover, when infected with influenza virus, they can be killed by an H-2Kb-restricted, influenza virus-specific cytotoxic T cell line. These results show that expression of the H-2Kb gene product on the L-cell surface is sufficient to make it a target for specific T-cell killing.

The cellular receptor (CD4) of the human immunodeficiency virus is expressed on neurons and glial cells in human brain

The expression of the CD4 antigen in normal human brain was investigated in parallel by immunohistochemical and Northern blot analyses. With anti-CD4 antibodies detecting different epitopes of the molecule, CD4+ neurons were defined in the cerebellum, thalamus, and pons. CD4+ glial cells were identified in the thalamus and pons. CD4-specific mRNA was detected in all three subareas and in the hippocampus, while other subareas were negative. The CD4+ cells were negative with anti-T cell antibodies (anti-CD2 and anti-CD8), as well as with antimonocyte antibodies (M-M 522 and M-M 42).

Genetic and serological heterogeneity of the supertypic HLA-B locus specificities Bw4 and Bw6

Gene cloning and sequencing of the HLA-B locus split antigens B38 (B16.1) and B39 (B16.2) allowed localization of their subtypic as well as their public specificities HLA-Bw4 or -Bw6 to the alpha-helical region of the alpha 1 domain flanked by the amino acid positions 74-83. Comparison of their amino acid sequences with those of other HLA-B-locus alleles established HLA-Bw6 to be distinguished by Ser at residue 77 and Asn at residue 80. In contrast, HLA-Bw4 is characterized by at least seven different patterns of amino acid exchanges at positions 77 and 80-83. Reactivity patterns of Bw4- or Bw6-specific monoclonal antibodies reveal two alloantigenic epitopes contributing to the HLA-Bw4 or -Bw6 specificity residing next to the region of highest diversity of the alpha 1 domain.

Mgm101p is a novel component of the mitochondrial nucleoid that binds DNA and is required for the repair of oxidatively damaged mitochondrial DNA

Maintenance of mitochondrial DNA (mtDNA) during cell division is required for progeny to be respiratory competent. Maintenance involves the replication, repair, assembly, segregation, and partitioning of the mitochondrial nucleoid. MGM101 has been identified as a gene essential for mtDNA maintenance in S. cerevisiae, but its role is unknown. Using liquid chromatography coupled with tandem mass spectrometry, we identified Mgm101p as a component of highly enriched nucleoids, suggesting that it plays a nucleoid-specific role in maintenance. Subcellular fractionation, indirect immunofluorescence and GFP tagging show that Mgm101p is exclusively associated with the mitochondrial nucleoid structure in cells. Furthermore, DNA affinity chromatography of nucleoid extracts indicates that Mgm101p binds to DNA, suggesting that its nucleoid localization is in part due to this activity. Phenotypic analysis of cells containing a temperature sensitive mgm101 allele suggests that Mgm101p is not involved in mtDNA packaging, segregation, partitioning or required for ongoing mtDNA replication. We examined Mgm101p's role in mtDNA repair. As compared with wild-type cells, mgm101 cells were more sensitive to mtDNA damage induced by UV irradiation and were hypersensitive to mtDNA damage induced by gamma rays and H2O2 treatment. Thus, we propose that Mgm101p performs an essential function in the repair of oxidatively damaged mtDNA that is required for the maintenance of the mitochondrial genome.

Identification of HLA-B27-restricted peptides from the Chlamydia trachomatis proteome with possible relevance to HLA-B27-associated diseases

The association of HLA-B27 with ankylosing spondylitis and reactive arthritis is the strongest one known between an MHC class I Ag and a disease. We have searched the proteome of the bacterium Chlamydia trachomatis for HLA-B27 binding peptides that are stimulatory for CD8(+) cells both in a model of HLA-B27 transgenic mice and in patients. This was done by combining two biomathematical computer programs, the first of which predicts HLA-B27 peptide binding epitopes, and the second the probability of HLA-B27 peptide generation by the proteasome system. After preselection, immunodominant peptides were identified by Ag-specific flow cytometry. Using this approach we have identified for the first time nine peptides derived from different C. trachomatis proteins that are stimulatory for CD8(+) T cells. Eight of these nine murine-derived peptides were recognized by cytotoxic T cells. The same strategy was used to identify B27-restricted chlamydial peptides in three patients with reactive arthritis. Eleven peptides were found to be stimulatory for patient-derived CD8(+) T cells, of which eight overlapped those found in mice. Additionally, we applied the tetramer technology, showing that a B27/chlamydial peptide containing one of the chlamydial peptides stained CD8(+) T cells in patients with Chlamydia-induced arthritis. This comprehensive approach offers the possibility of clarifying the pathogenesis of B27-associated diseases.