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991.
The minichromosome maintenance assay isfrequently used to characterize mutations genetically that affect the initiation of DNA replication or to decipherfunctional components in autonomously replicating sequences. The assay determines minichromosome loss by measuring the percentage of plasmid-containing cells in cultures after a period of growth in nonselective medium. Here we analyze data acquisition errors that contribute to the low accuracy of the routine versions of the assay. We propose modifications that eliminate errors in the acquisition of two variables and significantly improve the accuracy of the assay. 相似文献
992.
We describe a chemo-enzymatic synthesis of 3'- and 6'-O-sialyllactose, two trisaccharides occurring in the 'acidic fraction' of the human milk oligosaccharides and endowed with potential antiadhesive activity. The key step is the highly regioselective 6'-O-acylation of benzyllactoside, which gave access to suitably protected lactose building blocks to be used as acceptors in the sialylation reaction. Moreover, the synthesis of the carboxymethyl and sulfo analogues of the title compounds is reported. 相似文献
993.
The gypsy moth, Lymantria dispar, produces two structurally and genetically distinct types of spermatozoa. The eupyrene spermatozoa are genetically haploid and structurally typical. The apyrene spermatozoa are anucleate and structurally different from eupyrene spermatozoa. To understand further the events contributing to meiotic chromosome missegregation in apyrene spermatocytes, we examined the progression of meiosis in these cells with respect to their eupyrene counterparts. Chromosomal bouquet formation and fusion of nucleolar organizing regions are disrupted in apyrene nuclei. In addition, the chromatin of apyrene nuclei is prematurely and extremely condensed compared with that of eupyrene nuclei. An antibody to the conserved synaptonemal complex protein 3 (SCP3) labeled eupyrene pachytene chromosomes, but not apyrene pachytene chromosomes. In addition, apyrene meiotic spindles are missing a subset of microtubules, which likely include kinetochore microtubules. Because the condensation behavior of meiotic chromatin in apyrene spermatocytes deviates from that of eupyrene spermatocytes, we examined the appearance and distribution of the phosphorylated form of histone H3, but no significant differences in histone H3 phosphorylation were found between apyrene and eupyrene spermatocytes. We argue that because a pachytene checkpoint is not initiated in apyrene spermatocytes, this system may provide a way to understand better the underlying biochemical connections between pairing, recombination, synapsis, kinetochore assembly and segregation of chromosomes during meiosis in a higher eukaryote. 相似文献
994.
995.
Identification of a non-canonical tyrosine-based endocytic motif in an ionotropic receptor 总被引:4,自引:0,他引:4
Royle SJ Bobanović LK Murrell-Lagnado RD 《The Journal of biological chemistry》2002,277(38):35378-35385
Rapid modulation of the surface number of certain ionotropic receptors is achieved by altering the relative rates of insertion and internalization. These receptors are internalized by a clathrin-mediated pathway; however, a motif that is necessary for endocytosis of ionotropic receptors has not yet been identified. Here, we identified a motif that is required for constitutive and agonist-regulated internalization of the ionotropic P2X(4) receptor. Three amino acids in the C terminus of P2X(4) (Tyr(378), Gly(381), and Leu(382)) compose a non-canonical tyrosine-based sorting signal of the form YXXGL. We found that P2X(4) protein was present in clathrin-coated vesicles isolated from rat brain and that a glutathione S-transferase fusion of the P2X(4) C terminus pulled down the adaptor protein-2 complex from brain extract. Mutation of either the tyrosine-binding pocket of the mu2 subunit of adaptor protein-2 or the YXXGL motif in the receptor C terminus caused a decrease in receptor internalization and a dramatic increase in the surface expression of P2X(4) receptors. The YXXGL motif represents a non-canonical tyrosine-based sorting signal that is necessary for efficient endocytosis of the P2X(4) receptor. Similar motifs are present in other receptors and may be important for the control of their functional expression. 相似文献
996.
Crystal structure of a major secreted protein of Mycobacterium tuberculosis-MPT63 at 1.5-A resolution
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Goulding CW Parseghian A Sawaya MR Cascio D Apostol MI Gennaro ML Eisenberg D 《Protein science : a publication of the Protein Society》2002,11(12):2887-2893
MPT63 is a small, major secreted protein of unknown function from Mycobacterium tuberculosis that has been shown to have immunogenic properties and has been implicated in virulence. A BLAST search identified that MPT63 has homologs only in other mycobacteria, and is therefore mycobacteria specific. As MPT63 is a secreted protein, mycobacteria specific, and implicated in virulence, MPT63 is an attractive drug target against the deadliest infectious disease, tuberculosis (TB). As part of the TB Structural Genomics Consortium, the X-ray crystal structure of MPT63 was determined to 1.5-Angstrom resolution with the hope of yielding functional information about MPT63. The structure of MPT63 is an antiparallel beta-sandwich immunoglobulin-like fold, with the unusual feature of the first beta-strand of the protein forming a parallel addition to the small antiparallel beta-sheet. MPT63 has weak structural similarity to many proteins with immunoglobulin folds, in particular, Homo sapiens beta2-adaptin, bovine arrestin, and Yersinia pseudotuberculosis invasin. Although the structure of MPT63 gives no conclusive evidence to its function, structural similarity suggests that MPT63 could be involved in cell-host interactions to facilitate endocytosis/phagocytosis. 相似文献
997.
998.
Few resources are available to guide public health officials in investigations of reported birth defects clusters. The majority of published resources focus on the investigation of cancer and infectious disease clusters and do not address clinical and epidemiologic concerns specific to birth defects research. This document aims to address these concerns, discuss the needs of the affected community, and provide suggestions for the development of a standardized protocol to be used as a guide in the investigation of birth defects clusters. We suggest that health departments and birth defects registries that may receive reports of birth defects clusters establish a protocol for responding that includes the following steps: develop a proactive plan for future birth defects cluster reports (step I), receive report of a birth defects cluster (step II), verify diagnoses and complete case ascertainment (step III), compare the observed rate to a reference rate (step IV), ascertain exposures among cases from available records (step V), interview case mothers (step VI), initiate further epidemiologic study-selection of controls (step VII), and communicate results to the community (step VIII). Specific criteria for continuing or terminating an investigation should be established before receiving cluster reports. The recommendations in this report should be carefully considered to ensure that the specific needs of the region, agency and affected community are met. 相似文献
999.
Martínez de Villarreal L Pérez JZ Vázquez PA Herrera RH Campos Mdel R López RA Ramírez JL Sánchez JM Villarreal JJ Garza MT Limón A López AG Bárcenas M García JR Domínguez AS Nuñez RH Ayala JL Martínez JG González MT Alvarez CG Castro RN 《Teratology》2002,66(5):249-256
BACKGROUND: Nuevo León is a state in northeastern Mexico, near the border of Texas. Mean mortality rate from 1996-98 due to anencephaly cases was 0.6/1,000. In 1999 a surveillance program for the registry and prevention of neural tube defects (NTD) cases was initiated. METHODS: Cases were obtained from hospitals and OB-GYN clinics by immediate notification, death certificates, or fetal death registries. Only isolated cases of NTD were included. In August 1999 a folic acid campaign was initiated with the free distribution of the vitamin to low-income women with a recommendation to take a 5.0-mg pill once a week. Number of cases and rates from 1999 to 2001 were compared (chi(2) test). RESULTS: After 2 years there has been a significant reduction in the number of cases and rates. In 1999 there were 95 NTD cases and in the years 2000 and 2001 there were only 59 and 55 respectively (P < 0.001). NTD rate decreased from 1.04/1,000 in 1999 to 0.58/1,000 in 2001. Anencephaly and spina bifida rates decreased from 0.55/1,000 to 0.29/1,000 and from 0.47/1,000 to 0.22/1,000 respectively, from 1999-2001. Decrease of female cases was higher than male cases for both phenotypes. CONCLUSION: After 2 years there was a 50% decrease in the incidence of anencephaly and spina bifida cases with a significant reduction of infant mortality and disability. These results encourage us to propose the use of a single tablet of 5.0-mg of folic acid per week as an alternative to supplementation on a daily basis. 相似文献
1000.
Intra- and interspecific contact rates of 12 adult (five females, seven males) raccoons (Procyon lotor) were recorded while these animals fed at a rural garbage dump 40 km north of Kingston, Ontario, Canada from 15 June to 5 September 1995. While raccoons were being observed, they bit, and were bitten, by their conspecifics an average of 0.99 (+/- 0.21) and 1.28 (+/- 0.21) times per hour, respectively, while feeding. Based on mean nightly contact rates (which included time when raccoons were not observed), raccoons bit one of their conspecifics once every 3 nights while feeding. The mean rate of bites made and received per hour for males was not significantly different from lactating females. There was no detectable difference between the mean rate of bites made and received per hour for raccoons which regularly versus occasionally fed at the dump. No interspecific contacts were observed, though raccoons and striped skunks (Mephitis mephitis) often fed at the dump concurrently. The contact rates in this study are the first to be calculated for raccoons directly from field data and will be useful as a point of reference for modeling rabies spread in raccoons in areas with similar site characteristics. 相似文献