分类: 生物学 >> 生物物理学 提交时间: 2016-05-11
摘要: Although there have been many investigations into how trinucleotide repeats affect nucleosome formation and local chromatin structure, the nucleosome positioning of GAA triplet-repeats in the human genome has remained elusive. In this work, the nucleosome occupancy around GAA triplet-repeats across the human genome was computed statistically. The results showed a nucleosome-depleted region in the vicinity of GM triplet-repeats in activated and resting CD4(+) T cells. Furthermore, the A-tract was frequently adjacent to the upstream region of GM triplet-repeats and could enhance the depletion surrounding GAA triplet-repeats. In vitro chromatin reconstitution assays with GM-containing plasmids also demonstrated that the inserted GAA triplet-repeats destabilized the ability of recombinant plasmids to assemble nucleosomes. Our results suggested that GM triplet-repeats have lower affinity to histones and can change local nucleosome positioning. These findings may be helpful for understanding the mechanism of Friedreich's ataxia, which is associated with GM triplet-repeats at the chromatin level. (C) 2015 Elsevier Inc All rights reserved.
分类: 生物学 >> 生物物理学 提交时间: 2016-05-12
摘要: The aim of this study was to characterize the quinolone resistance of Salmonella enterica serovar Indiana isolated from chickens in China. A total of 293 Salmonella strains were isolated from chicken farms and slaughterhouses in Shandong province of China, and 130 (44.4%) were characterized as Salmonella enterica Indiana (chicken farms, n = 52 strains; slaughter houses, n = 78 strains). All isolate serotypes were tested with the Kauffmann-White classification system and examined for susceptibility to the quinolones: nalidixic acid, enrofloxacin, norfloxacin, and ciprofloxacin. The resistance of the Salmonella Indiana strains to nalidixic acid, enrofloxacin, norfloxacin, and ciprofloxacin were 100, 73.1, 71.2, and 82.7%, and 100, 59.0, 79.5, and 80.2%, respectively. Selected quinolone resistant strains were evaluated for mutations in genes (gyrA, gyrB, parC, and marA) by DNA sequencing. The gyrA mutation was found in all isolates, the parC mutation was only found in some isolates, and the gyrB and marA mutations were not observed. Quinolone resistance was evaluated in the representative isolates by screening for the quinolone resistance determinants, qnrA, qnrB, qnrS, qepA, and aac (6')-Ib-cr using PCR technology. The quinolone resistance determinants in Salmonella, qnrA, qnrB, qnrS, and qepA were negative by PCR, but aac(6')-Ib-cr had high detection rates of 90.4 and 96.2% in chicken farms and slaughterhouses, respectively. Salmonella Indiana containing the gyrA mutation was prevalent in farms and slaughterhouses and possessed a high frequency of the quinolone resistance determinant aac(6')-Ib-cr. These bacteria may have originated from the same source.
分类: 生物学 >> 生物物理学 >> 生物物理、生物化学与分子生物学 提交时间: 2016-05-18
摘要: Autophagosome formation is promoted by the PI3 kinase complex and negatively regulated by myotubularin phosphatases, indicating that regulation of local phosphatidylinositol 3-phosphate (PtdIns3P) levels is important for this early phase of autophagy. Here, we show that the Caenorhabditis elegans myotubularin phosphatase MTM-3 catalyzes PtdIns3P turnover late in autophagy. MTM-3 acts downstream of the ATG-2/EPG-6 complex and upstream of EPG-5 to promote autophagosome maturation into autolysosomes. MTM-3 is recruited to autophagosomes by PtdIns3P, and loss of MTM-3 causes increased autophagic association of ATG-18 in a PtdIns3P-dependent manner. Our data reveal critical roles of PtdIns3P turnover in autophagosome maturation and/or autolysosome formation.