Nielsen O, Egel R
Institute of Genetics, University of Copenhagen, Denmark.
EMBO J. 1989 Jan;8(1):269-76. doi: 10.1002/j.1460-2075.1989.tb03373.x.
In fission yeast mating-type switching is initiated by the formation of a double-strand DNA break at the mating-type locus. A prerequisite for generation of the break is some 'imprinting' of the DNA in the previous cell cycle. We have used the technique of genomic sequencing to map the position of the break directly on chromosomal DNA cleaved in vivo. On one strand the break is situated very close to the right-hand border of the expressed mat1 cassette. Cells of opposite mating type, P and M, have their breaks at slightly different positions on this strand. On the other DNA strand of both alleles the ends are probably masked by tightly bound proteins and therefore the precise nature of the break could not be determined. Since the break is stable throughout the cell cycle, these proteins may function in vivo to confer structural stability on the chromosomes having the break. The implications of these findings for models of mating-type switching are discussed.
在裂殖酵母中，交配型转换是由交配型基因座处双链DNA断裂的形成引发的。产生该断裂的一个先决条件是在前一个细胞周期中对DNA进行某种“印记”。我们利用基因组测序技术直接在体内切割的染色体DNA上定位断裂的位置。在一条链上，断裂位点非常靠近表达的mat1盒的右侧边界。相反交配型的细胞，P型和M型，在这条链上的断裂位置略有不同。在两个等位基因的另一条DNA链上，末端可能被紧密结合的蛋白质掩盖，因此无法确定断裂的确切性质。由于断裂在整个细胞周期中都是稳定的，这些蛋白质可能在体内发挥作用，赋予具有断裂的染色体结构稳定性。讨论了这些发现对交配型转换模型的意义。
