A mutant of Escherichia coil with increased
There are numerous examples of the regular segregation of achiasmate chromosomes at meiosis I in Drosophila melanogaster females. Classically, the choice of achiasmate segregational partners has been thought to be independent of homology, but rather made on the basis of availability or similarities in size and shape. To the contrary, we show here that heterochromatic homology plays a primary role in ensuring the proper segregation of achiasmate homologs. We observe that the heterochromatin of chromosome 4 functions as, or contains, a meiotic pairing site. We show that free duplications carrying the 4th chromosome pericentric heterochromatin induce high frequencies of 4th chromosome nondisjunction regardless of their size. Moreover, a duplication from which some of the 4th chromosome heterochromatin has been removed is unable to induce 4th chromosome nondisjunction. Similarly, in the absence of either euchromatic homology or a size similarity, duplications bearing the X chromosome heterochromatin also disrupt the segregation of two achiasmate X chromosome centromeres. Although heterochromatic regions are sufficient to conjoin nonexchange homologues, we confirm that the segregation of heterologous chromosomes is determined by size, shape, and availability. The meiotic mutation Axs differentiates between these two processes of achiasmate centromere coorientation by disrupting only the homology-dependent mechanism. Thus there are two different mechanisms by which achiasmate segregational partners are chosen. We propose that the absence of diplotene-diakinesis during female meiosis allows heterochromatic pairings to persist until prometaphase and thus to co-orient homologous centromeres. We also propose that heterologous disjunctions result from a separate and homology-independent process that likely occurs during prometaphase. The latter process, which may not require the physical association of segregational partners, is similar to those observed in many insects, in Saccharomyces cerevisiae and in C. elegans males. We also suggest that the physical basis of this process may reflect known properties of the Drosophila meiotic spindle.
We present a scheme for locating double‐strand breaks (DSBs) in meiotic chromosomes of Saccharomyces cerevisiae, based on the separation of large DNA molecules by pulsed field gel electrophoresis. Using a rad50S mutant, in which DSBs are not processed, we show that DSBs are widely induced in S. cerevisiae chromosomes during meiosis. Some of the DSBs accumulate at certain preferred sites. We present general profiles of DSBs in chromosomes III, V, VI and VII. A map of the 12 preferred sites on chromosome III is presented. At least some of these sites correlate with known ‘hot spots’ for meiotic recombination. The data are discussed in view of current models of meiotic recombination and chromosome segregation.
Biofilms are found in many water supply systems where they form an environment in which different bacteria can be entrapped for long periods. Besides the aesthetic aspect, biofilm has a major contribution in biocorrosion, disinfection inefficiency and possibly may act as a reservoir for pathogenic and non-pathogenic microorganisms. In the present study, two pathogenic bacteria Legionella pneumophila and Salmonella typhimurium WG-49 were introduced into a biofilm simulation flow system supplied with sterile and non-sterile tap water. The survival of these microorganisms into the biofilm formed on glass and PVC coupons at two temperatures (24°C and 36°C) was compared in this system. On glass supports, under sterile conditions at 36°C, Legionella pneumophila sg3 decreased by 6 logs during 40d continuous recirculation. Under non-sterile conditions, L. pneumophila decreased by only half log <48d. S. typhimurium WG-49 under the same conditions showed an increase of 3 logs in the sterile system for 31d, while in the non-sterile system it dropped by only 0.5 log for 20d. At 24°C, L. pneumophila remained stable for >40d under sterile conditions. In non-sterile conditions, L. pneumophila dropped by 1 log for 35d. S. typhimurium, in a sterile system, remained almost unchanged, while in the non-sterile system an increase of 3 logs was observed for the first 21d and thereafter a decrease of 2 logs for the next 21d of the experiment. L. pneumophila on PVC coupons at 36°C survived better compared with glass support. The experimental data show that survival of pathogenic microorganisms into biofilm is variable and depends on many factors, making the survival prediction a difficult task. However, the survival results of L. pneumophila and S. typhimurium in time terms should raise important questions on their potential threat in water distribution systems.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.