Unrau P, Johnson J R
Chalk River Laboratories, Atomic Energy of Canada, Ltd, Ontario, Canada.
J Theor Biol. 1995 Nov 7;177(1):73-86. doi: 10.1006/jtbi.1995.0226.
Induced mitotic gene conversion studies on the CYC1 gene of yeast have shown that the actual base pair changes, the types of changes (base substitution, deletion or addition) and the distances between mutations all affect gene conversion yields. In crosses between mutations less than four bases apart, gene conversion rates are as low as back mutation rates. The same mutants crossed to alleles more than five bases away may recombine 50-fold more. In crosses between mutations five or more base pairs apart, recombination rates varying by up to ten-fold are observed when comparing mutations at the same codon sites. The actual mutations in crosses affect recombination rates at these distances. The data rules out models in which mutants are repaired independently. Models with large gaps at the initiation site are ruled out if the mutants are within the gap. Recombination models are favoured in which both mutations can interact at a distance to affect the probability of recombination; such interactions may reflect the geometry of the recombinational junctions. The specific interactions proposed are that the actual mutations, and residual mismatches arising on excision resynthesis, affect both the further migration of the recombinational junction, and the probability that excision-repair will detect and correct residual mismatches. Junction models in which interactions are expected include those composed of base tetraplexes. The data is interpreted in terms of these models. Meiotic recombination data is consistent with these models.
对酵母CYC1基因进行的诱导有丝分裂基因转换研究表明，实际的碱基对变化、变化类型（碱基替换、缺失或添加）以及突变之间的距离都会影响基因转换率。在相距少于四个碱基的突变之间进行杂交时，基因转换率与回复突变率一样低。与相距超过五个碱基的等位基因杂交时，相同的突变体可能会有多达50倍的重组。在相距五个或更多碱基对的突变之间进行杂交时，比较相同密码子位点的突变，观察到重组率变化高达十倍。杂交中的实际突变会影响这些距离处的重组率。这些数据排除了突变体独立修复的模型。如果突变体位于间隙内，则排除起始位点存在大间隙的模型。有利于这样的重组模型：两个突变都可以在一定距离处相互作用以影响重组的概率；这种相互作用可能反映了重组连接点的几何形状。提出的具体相互作用是，实际的突变以及切除再合成时产生的残留错配，既影响重组连接点的进一步迁移，也影响切除修复检测和纠正残留错配的概率。预期会有相互作用的连接点模型包括由碱基四重体组成的模型。根据这些模型对数据进行了解释。减数分裂重组数据与这些模型一致。
