Lichten M, Haber J E
Laboratory of Biochemistry, National Cancer Institute, Bethesda, Maryland 20892.
Genetics. 1989 Oct;123(2):261-8. doi: 10.1093/genetics/123.2.261.
We have examined the role that genomic location plays in mitotic intragenic recombination. Mutant alleles of the LEU2 gene were inserted at five locations in the yeast genome. Diploid and haploid strains containing various combinations of these inserts were used to examine both allelic recombination (between sequences at the same position on parental homologs) and ectopic recombination (between sequences at nonallelic locations). Chromosomal location had little effect on mitotic allelic recombination. The rate of recombination to LEU2 at five different loci varied less than threefold. This finding contrasts with previous observations of strong position effects in meiosis; frequencies of meiotic recombination at the same five loci differ by about a factor of forty. Mitotic recombination between dispersed copies of leu2 displayed strong position effects. Copies of leu2 located approximately 20 kb apart on the same chromosome recombined at rates 6-13-fold higher than those observed for allelic copies of leu2. leu2 sequences located on nonhomologous chromosomes or at distant loci on the same chromosome recombined at rates similar to those observed for allelic copies. We suggest that, during mitosis, parental homologs interact with each other no more frequently than do nonhomologous chromosomes.
我们研究了基因组位置在有丝分裂基因内重组中所起的作用。将LEU2基因的突变等位基因插入酵母基因组的五个位置。利用含有这些插入片段不同组合的二倍体和单倍体菌株来检测等位基因重组（亲本同源染色体上相同位置的序列之间）和异位重组（非等位位置的序列之间）。染色体位置对有丝分裂等位基因重组影响很小。在五个不同位点向LEU2的重组率变化不到三倍。这一发现与之前在减数分裂中观察到的强烈位置效应形成对比；在相同的五个位点，减数分裂重组频率相差约40倍。leu2分散拷贝之间的有丝分裂重组表现出强烈的位置效应。位于同一条染色体上相距约20 kb的leu2拷贝，其重组率比leu2等位拷贝的重组率高6至13倍。位于非同源染色体上或同一条染色体上远距离位点的leu2序列，其重组率与等位拷贝的重组率相似。我们认为，在有丝分裂期间，亲本同源染色体之间的相互作用频率并不比非同源染色体之间的相互作用频率更高。
