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These phenotypes are similar to those of rad21-K1 and are significantly enhanced in a hsk1-89 rad21-K1 double mutant. hsk1-89 displays apparent defect in mitosis at 37☌ leading to accumulation of cells with near 2C DNA content and with aberrant nuclear structures. Furthermore, Cds1-dependent hyperphosphorylation of Dfp1 in response to hydroxyurea arrest is eliminated in hsk1-89, suggesting that sufficient activation of Hsk1-Dfp1 kinase is required for S phase entry and replication checkpoint signaling. Cds1 kinase activation, which normally occurs in response to early S phase arrest by nucleotide deprivation, is largely impaired in hsk1-89. hsk1-89 displays synthetic lethality in combination with rad3 deletion, indicating that survival of hsk1-89 depends on Rad3-dependent checkpoint pathway. Checkpoint defect in hsk1-89 is indicated by accumulation of cut cells at 30☌. Analyses of a newly isolated temperature-sensitive mutant, hsk1-89, reveal that Hsk1 plays crucial roles in DNA replication checkpoint signaling and maintenance of proper chromatin structures during mitotic S phase through regulating the functions of Rad3 (ATM)-Cds1 and Rad21 (cohesin), respectively, in addition to expected essential roles for initiation of mitotic DNA replication through phosphorylating Cdc19 (Mcm2). Possible sources for the sex-specific differences in meiotic prophase kinetics are discussed.read more read lessĪbstract: Hsk1, Saccharomyces cerevisiae Cdc7-related kinase in Shizosaccharomyces pombe, is required for G1/S transition and its kinase activity is controlled by the regulatory subunit Dfp1/Him1. On the other hand, meiotic prophase for sperm production in males is completed by 20-24 h. Further, we find that the duration of the pachytene sub-stage is modulated by the presence of sperm. Meiotic prophase for oocyte production in hermaphrodites lasts 54-60 h. Finally, we have exploited S-phase labeling to monitor the timing of progression through meiotic prophase. Furthermore, our assay reveals that different regions of the genome replicate at different times, with the heterochromatic-like X chromosomes replicating at a distinct time from the autosomes. Using mutants that affect the mitosis/meiosis switch, we show that meiotic S phase is at least twice as long as mitotic S phase in C. We have developed an assay to monitor DNA replication in vivo in mitotic and meiotic germline nuclei of the nematode Caenorhabditis elegans. DSBs are not sufficient for the appearance of Rad51 foci Rad52, Rad55, and Rad57 are also required supporting a model in which these three proteins promote meiotic recombination by promoting the assembly of strand exchange complexes.read more read lessĪbstract: The replication of chromosomes in meiosis is an important first step for subsequent chromosomal interactions that promote accurate disjunction in the first of two segregation events to generate haploid gametes.

Mutants that lack Spo11, a protein required for DSB formation, are defective in focus formation, and this defect is suppressed by ionizing radiation in a dose-dependent manner.

Double-strand breaks (DSBs) promote formation of RPA, Rad52, and Rad51 foci. In addition, RPA foci are observed during mitotic S phase. Rad52 and RPA foci are distinct from those formed by Rad51, and its meiosis-specific relative Dmc1, in that they are also detected in meiosis during replication. Immunostaining shows extensive colocalization of Rad52 and RPA and more limited colocalization of Rad52 with the strand exchange protein Rad51. Replication of DNA in prokaryotes begins at a single origin of replication, shown in the figure to the left, and proceeds in a bidirectional manner around the circular chromosome until replication is complete.Abstract: We show that the Saccharomyces cerevisiae recombination protein Rad52 and the single-strand DNA-binding protein RPA assemble into cytologically detectable subnuclear complexes (foci) during meiotic recombination.