Hamza H, Haedens V, Mekki-Berrada A, Rossignol J L
Proc Natl Acad Sci U S A. 1981 Dec;78(12):7648-51. doi: 10.1073/pnas.78.12.7648.
G234 is a silent mutation located in the middle of gene b2, which controls spore pigmentation in Ascobolus immersus. Its effect on the aberrant segregation patterns of while spore mutants located in the same gene was investigated. When heterozygous, G234 decreases the frequency of aberrant segregations of the mutants located on its right, toward the low conversion end. It almost completely suppresses the aberrant 4:4 asci for mutants giving postmeiotic segregation and decreases the disparity between the 6 wild-type:2 mutant and 2 wild-type:6 mutant aberrant asci for mutants giving only these types of convertant asci. These effects are polar; G234 does not change the aberrant segregation pattern of the mutants located on its left, toward the high conversion end. This behavior suggests that G234 blocks the migration of the symmetric phase of hybrid DNA that diffuses from the high conversion end but does not prevent the formation of asymmetrical hybrid DNA. Taking into account previous observations, we conclude that the high conversion end corresponds to a region of asymmetric initiation of recombination rather than to a region of preferential ending of recombination. The asymmetric hybrid DNA first formed is further changed into a symmetric phase that extends via branch migration toward the low conversion end.
G234是位于基因b2中部的一个沉默突变，该基因控制浸没盘菌的孢子色素沉着。研究了它对位于同一基因中的白色孢子突变体异常分离模式的影响。杂合时，G234会降低位于其右侧、朝向低转化率端的突变体异常分离的频率。对于产生减数分裂后分离的突变体，它几乎完全抑制了异常的4:4子囊，并减小了产生仅这些类型转化子囊的突变体在6个野生型:2个突变体和2个野生型:6个突变体异常子囊之间的差异。这些效应是极性的；G234不会改变位于其左侧、朝向高转化率端的突变体的异常分离模式。这种行为表明，G234阻断了从高转化率端扩散而来的杂种DNA对称阶段的迁移，但不阻止不对称杂种DNA的形成。考虑到之前的观察结果，我们得出结论，高转化率端对应于重组不对称起始的区域，而不是重组优先终止的区域。最初形成的不对称杂种DNA会进一步转变为对称阶段，该对称阶段通过分支迁移向低转化率端延伸。
