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Examines the effects of ultraviolet rays in Schizosaccharomyces pombe cells. Elevation of mitotic recombination and cell cycle; Determination on the UV damage induced mitotic intrachromosomal recombination; Frequency of spontaneous recombination to cell death. more...

Describes the introduction of a double-strand break to induce mitotic intrachromosomal recombination in the fission yeast Schizosaccharomyces pombe. Nontandem direct repeats of ade6 heteroalleles as recombination substrates; Determining of spontaneous recombinant frequencies by fluctuation tests; Isolation of DSB-induced red/white half-sectored colonies. more...

Meiotic recombination enhances genetic diversity as well as ensures proper segregation of homologous chromosomes, requiring Spo11-initiated double-strand breaks (DSBs). DNA deaminases act on regions of single-stranded DNA and deaminate cytosine to uracil (dU). In the immunoglobulin locus, this lesion will initiate point imitations, gene conversion, and DNA recombination. To begin to delineate the effect of induced base lesions on meiosis, we analyzed the effect of expressing DNA deaminases (activation-induced deaminase, AID, and APOBEC3C) in germ cells. We show that meiotic dU:dG lesions can partially rescue a spo11Δ phenotype in yeast and worm. In rec12 Schizosaccharomyces pombe, AID expression increased proper chromosome segregation, thereby enhancing spore viability, and induced low-frequency meiotic crossovers. Expression of AID in the germ cells of Caenorhabditis elegans spo-11 induced meiotic RAD-51 foci formation and chromosomal bivalency and segregation, as well as an increase in viability. RNAi experiments showed that this rescue was dependent on uracil DNA-glycosylase (Ung). Furthermore, unlike ionizing radiation-induced spo-11 rescue, AID expression did not induce large numbers of DSBs during the rescue. This suggests that the products of DNA deamination and base excision repair, such as uracil, an abasic site, or a single-stranded nick, are sufficient to initiate and alter meiotic recombination in uni- and multicellular organisms. [ABSTRACT FROM AUTHOR] more...