Miesel L, Segall A, Roth J R
Department of Biology, University of Utah, Salt Lake City 84112.
Genetics. 1994 Aug;137(4):919-32. doi: 10.1093/genetics/137.4.919.
Homologous sequences placed in inverse order at particular separated sites in the bacterial chromosome (termed "permissive") can recombine to form an inversion of the intervening chromosome segment. When the same repeated sequences flank other chromosome segments ("non-permissive"), recombination occurs but the expected inversion rearrangement is not found among the products. The failure to recover inversions of non-permissive chromosomal segments could be due to lethal effects of the final rearrangement. Alternatively, local chromosomal features might pose barriers to reciprocal exchanges between sequences at particular sites and could thereby prevent formation of inversions of the region between such sites. To distinguish between these two possibilities, we have constructed inversions of two non-permissive intervals by means of phage P22-mediated transduction crosses. These crosses generate inversions by simultaneous incorporation of two transduced fragments, each with a sequence that forms one join-point of the final inversion. We constructed inversions of the non-permissive intervals trp ('34) to his ('42) and his ('42) to cysA ('50). Strains with the constructed inversions are viable and grow normally. These results show that our previous failure to detect formation of these inversions by recombination between chromosomal sequences was not due to lethal effects of the final rearrangement. We infer that the "non-permissive" character of some chromosomal segments reflects the inability of the recombination system to perform the needed exchanges between inverse order sequences at particular sites. Apparently these mechanistic problems were circumvented by the transductional method used here to direct inversion formation.
位于细菌染色体特定分离位点且顺序相反的同源序列（称为“允许的”）可发生重组，形成中间染色体片段的倒位。当相同的重复序列位于其他染色体片段两侧（“不允许的”）时，会发生重组，但在产物中未发现预期的倒位重排。未能恢复不允许的染色体片段的倒位可能是由于最终重排的致死效应。或者，局部染色体特征可能对特定位点的序列之间的相互交换构成障碍，从而可能阻止这些位点之间区域的倒位形成。为了区分这两种可能性，我们通过噬菌体P22介导的转导杂交构建了两个不允许区间的倒位。这些杂交通过同时整合两个转导片段产生倒位，每个片段都有一个形成最终倒位的一个连接点的序列。我们构建了从trp（‘34）到his（‘42）以及从his（‘42）到cysA（‘50）的不允许区间的倒位。具有构建的倒位的菌株是有活力的，并且正常生长。这些结果表明，我们之前未能通过染色体序列之间的重组检测到这些倒位的形成，并非由于最终重排的致死效应。我们推断，一些染色体片段的“不允许”特性反映了重组系统无法在特定位点的反向序列之间进行所需的交换。显然，这里用于直接形成倒位的转导方法规避了这些机制问题。
