Godwin A R, Liskay R M
Department of Genetics, Yale University School of Medicine, New Haven, Connecticut 06510.
Genetics. 1994 Feb;136(2):607-17. doi: 10.1093/genetics/136.2.607.
We examined the effects of insertion mutations on intrachromosomal recombination. A series of mouse L cell lines carrying mutant herpes simplex virus thymidine kinase (tk) heteroalleles was generated; these lines differed in the nature of their insertion mutations. In direct repeat lines with different large insertions in each gene, there was a 20-fold drop in gene conversion rate and only a five-fold drop in crossover rate relative to the analogous rates in lines with small insertions in each gene. Surprisingly, in direct repeat lines carrying the same large insertion in each gene, there was a larger drop in both types of recombination. When intrachromosomal recombination between inverted repeat tk genes with different large insertions was examined, we found that the rate of gene conversion dropped five-fold relative to small insertions, while the rate of crossing over was unaffected. The differential effects on conversion and crossing over imply that gene conversion is more sensitive to insertion mutation size. Finally, the fraction of gene conversions associated with a crossover increased from 2% for inverted repeats with small insertions to 18% for inverted repeats with large insertions. One interpretation of this finding is that during intrachromosomal recombination in mouse cells long conversion tracts are more often associated with crossing over.
我们研究了插入突变对染色体内重组的影响。构建了一系列携带突变单纯疱疹病毒胸苷激酶（tk）异等位基因的小鼠L细胞系；这些细胞系的插入突变性质各不相同。在每个基因中具有不同大插入片段的同向重复细胞系中，与每个基因中具有小插入片段的细胞系相比，基因转换率下降了20倍，而交换率仅下降了5倍。令人惊讶的是，在每个基因中携带相同大插入片段的同向重复细胞系中，两种类型的重组下降幅度更大。当检测具有不同大插入片段的反向重复tk基因之间的染色体内重组时，我们发现基因转换率相对于小插入片段下降了5倍，而交换率未受影响。对转换和交换的不同影响表明基因转换对插入突变大小更为敏感。最后，与交换相关的基因转换比例从具有小插入片段的反向重复的2%增加到具有大插入片段的反向重复的18%。这一发现的一种解释是，在小鼠细胞的染色体内重组过程中，长转换片段更常与交换相关。
