Arcangioli B
Unité des Virus Oncogènes, URA 1644 du CNRS, Département des Biotechnologies, Institut Pasteur, Paris, France.
EMBO Rep. 2000 Aug;1(2):145-50. doi: 10.1093/embo-reports/kvd023.
The mating-type switching of the fission yeast, Schizosaccharomyces pombe, is highly regulated. Two consecutive asymmetric divisions are required to produce one mating-type switched cell among the four progeny. Using DNA density-gradient centrifugation we demonstrate that one-fourth of the mat1 DNA is not replicated by the conventional semi-conservative mode, but instead both DNA strands are synthesized de novo. Our data are consistent with a gene conversion event, initiated by a site- and strand-specific DNA break (SSB). We further demonstrate that the virgin switched mat1-containing chromatid no longer contained the nick, while it is reintroduced during the lagging strand synthesis of the mat1 locus on the sister chromatid. This finding establishes at the molecular level a firm experimental link between the phenotype and genotype in the process of asymmetric mating-type switching during mitotic divisions.
裂殖酵母粟酒裂殖酵母的交配型转换受到高度调控。需要连续两次不对称分裂才能在四个子代中产生一个交配型转换细胞。通过DNA密度梯度离心，我们证明mat1 DNA的四分之一不是通过传统的半保留模式复制的，而是两条DNA链都是从头合成的。我们的数据与由位点和链特异性DNA断裂（SSB）引发的基因转换事件一致。我们进一步证明，含有mat1的未转换染色单体不再含有切口，而在姐妹染色单体上mat1基因座的滞后链合成过程中重新引入了切口。这一发现从分子水平上在有丝分裂过程中不对称交配型转换过程的表型和基因型之间建立了牢固的实验联系。
