Haber J E, Leung W Y
Rosenstiel Center, Brandeis University, Waltham, MA 02254-9110, USA.
Proc Natl Acad Sci U S A. 1996 Nov 26;93(24):13949-54. doi: 10.1073/pnas.93.24.13949.
Various studies suggest that eukarytoic chromosomes may occupy distinct territories within the nucleus and that chromosomes are tethered to a nuclear matrix. These constraints might limit interchromosomal interactions. We have used a molecular genetic test to investigate whether the chromosomes of Saccharomyces cerevisiae exhibit such territoriality. A chromosomal double-strand break (DSB) can be efficiently repaired by recombination between flanking homologous repeated sequences. We have constructed a strain in which DSBs are delivered simultaneously to both chromosome III and chromosome V by induction of the HO endonuclease. The arrangement of partially duplicated HIS4 and URA3 sequences around each HO recognition site allows the repair of the two DSBs in two alternative ways: (i) the creation of two intrachromosomal deletions or (ii) the formation of a pair of reciprocal translocations. We show that reciprocal translocations are formed approximately as often as the pair of intrachromosomal deletions. Similar results were obtained when one of the target regions was moved from chromosome V to any of three different locations on chromosome XI. These results argue that the broken ends of mitotic chromosomes are free to search the entire genome for appropriate partners; thus, mitotic chromosomes are not functionally confined to isolated domains of the nucleus, at least when chromosomes are broken.
多项研究表明，真核生物染色体可能在细胞核内占据不同的区域，并且染色体与核基质相连。这些限制可能会限制染色体间的相互作用。我们使用了一种分子遗传学测试来研究酿酒酵母的染色体是否表现出这种区域性。染色体双链断裂（DSB）可以通过侧翼同源重复序列之间的重组有效地修复。我们构建了一个菌株，通过诱导HO内切酶，将DSB同时传递到III号染色体和V号染色体上。每个HO识别位点周围部分重复的HIS4和URA3序列的排列允许以两种替代方式修复两个DSB：（i）产生两个染色体内缺失或（ii）形成一对相互易位。我们表明，相互易位的形成频率与一对染色体内缺失的形成频率大致相同。当其中一个目标区域从V号染色体移动到XI号染色体上的三个不同位置中的任何一个时，也获得了类似的结果。这些结果表明，有丝分裂染色体的断裂末端可以自由地在整个基因组中寻找合适的配对；因此，有丝分裂染色体在功能上并不局限于细胞核的孤立区域，至少在染色体断裂时是这样。
