The DNA-repair mechanism referred to as non-homologous end-joining (NHEJ) involves the Ku proteins (Ku70 and Ku80), DNA ligase IV and Lif1/XRCC4. Meiotic cells down-regulate NHEJ, to favour homologous recombination. In the December 6 Nature, Maria Valencia and colleagues describe a mechanism for the down-regulation of NHEJ in meiosis-competent MATa/MATα diploid Saccharomycescerevisiae cells (Nature 2001, 414:666-669).

They found that LIF1 (encoding ligase-interfacing factor 1) expression was decreased in the diploid strain, but LIF1 overexpression only partially restored NHEJ. Microarray analysis of mating-type mutant strains led them to identify a novel gene, NEJ1 (non-homologous end-joining defective). Deletion of NEJ1 reduces NHEJ, and the gene is strongly mating-type-regulated. The promoter regions of both the LIF1 and NEJ1 genes contain binding sites for the Mata1-Matα2 repressor.

Valencia et al. suggest that NEJ1 affects the cellular localization of LIF1 during meoisis. It will be interesting to see whether similar regulation...

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