Summary Pathogenic Vibrio cholerae remains a major human health concern. V. cholerae has a characteristic curved rod morphology, with a longer outer face and a shorter inner face. Previously, the mechanism and function of this curvature were unknown. Here we identify and characterize CrvA, the first curvature determinant in V. cholerae. CrvA self-assembles into filaments at the inner face of cell curvature. Unlike traditional cytoskeletons, CrvA localizes to the periplasm, and thus could be considered a periskeletal element. To quantify how curvature forms, we developed QuASAR (Quantitative Analysis of Sacculus Architecture Remodeling), which measures subcellular peptidoglycan dynamics. QuASAR reveals that CrvA asymmetrically patterns peptidoglycan insertion rather than removal, causing more material insertion into the outer face than the inner face. Furthermore, crvA is quorum regulated and CrvA-dependent curvature increases at high cell density. Finally, we demonstrate that CrvA promotes motility in hydrogels and confers an advantage in host colonization and pathogenesis.

During meiosis, double-strand breaks (DSBs) lead to crossovers, thought to arise from the resolution of double Holliday junctions (HJs) by an HJ resolvase. In Schizosaccharomyces pombe, meiotic crossovers are produced primarily through a mechanism requiring the Mus81-Eme1 endonuclease complex. Less is known about the processes that produces crossovers during the repair of DSBs in mitotic cells. We employed an inducible DSB system to determine the role of Rqh1-Top3 and Mus81-Eme1 in mitotic DSB repair and crossover formation in S. pombe. In agreement with the meiotic data, crossovers are suppressed in cells lacking Mus81-Eme1. And relative to the wild type, rqh1⌬ cells show a fourfold increase in crossover frequency. This suppression of crossover formation by Rqh1 is dependent on its helicase activity. We found that the synthetic lethality of cells lacking both Rqh1 and Eme1 is suppressed by loss of swi5 ؉ , which allowed us to show that the excess crossovers formed in an rqh1⌬ background are independent of Mus81-Eme1. This result suggests that a second process for crossover formation exists in S. pombe and is consistent with our finding that deletion of swi5 ؉ restored meiotic crossovers in eme1⌬ cells. Evidence suggesting that Rqh1 also acts downstream of Swi5 in crossover formation was uncovered in these studies. Our results suggest that during Rhp51-dependent repair of DSBs, Rqh1-Top3 suppresses crossovers in the Rhp57-dependent pathway while Mus81-Eme1 and possibly Rqh1 promote crossovers in the Swi5-dependent pathway.Meiotic cells depend on crossovers for creating genomic rearrangements, a critical step in ensuring genomic vitality. In fact crossing over is essential for spore viability in yeasts, while in mouse cells, blocking crossing over leads to embryonic lethality (6,17,35). The classic model for crossing over was first suggested by Robin Holliday, who proposed that crossovers arose by resolution of Holliday junctions (HJs) (27). This model was later refined to include the resolution of a double HJ (dHJ), which remains the major model for crossover formation (48) (Fig.

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Despite the high homology between human immunodeficiency virus type-1 (HIV-1) and human immunodeficiency virus type-2 (HIV-2) reverse transcriptases (RTs), the ribonuclease H (RNase H) level of HIV-2 RT is lower than that of HIV-1 RT, while the DNA polymerase of both RTs is similar. We conducted mutagenesis of HIV-2 RT Gln294 (shown to control the RNase H activity level when modified to a Pro in the smaller p54 subunit and not in the larger p68 subunit) to various residues, and assayed the activities of all mutants. All exhibited an RNase H that is higher than the wild-type (WT) HIV-2 RT level, although the DNA polymerase of all mutants equals WT HIV-2 RT level. These results represent a unique case, where every mutation induces an increase rather than a decrease in an enzymeÕs activity.

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