Schmucker R, Ritthaler W, Stern B, Kamp D
J Gen Virol. 1986 Jun;67 ( Pt 6):1123-33. doi: 10.1099/0022-1317-67-6-1123.
Gin-mediated site-specific recombination promotes inversion of the G segment of phage Mu. The crossover takes place between two 34 bp-long inverted repeat sequences flanking the G segment. We have characterized the inversion site, the target for the site-specific recombination mechanism. An artificial invertible segment was constructed which consists of parts of the invertible segments of Mu and phage P1, which in this respect are largely homologous. Upon inversion of this hybrid segment the crossover site could be located, by DNA sequencing, in the ACCT sequence of the centre of symmetry in the inverted repeat in Mu. The hybrid Mu-P1 segment inverts at a lower frequency than its parental invertible segments probably because of the mismatches between the inverted repeats of Mu and P1. This suggests that base pairing between the inverted repeats is an intermediate step in recombination. Plasmids with subcloned G segments lacking the adjacent beta region of Mu or the corresponding region in P7, a relative of P1, are deficient in inversion. By analysis through site-specific mutagenesis of Mu DNA, an enhancer element with multiple recognition sites was identified which is necessary for efficient inversion. This component of the inversion site was located in a 170 bp segment within the Mu beta region, 30 bp to the right of the inverted repeat sequence, but can be separated from the crossover site by a 1200 bp insertion without losing its effect.
gin介导的位点特异性重组促进噬菌体Mu的G片段倒位。交叉发生在G片段两侧两个34bp长的反向重复序列之间。我们已经对倒位位点进行了表征，它是位点特异性重组机制的靶点。构建了一个人工可逆片段，它由Mu和噬菌体P1的可逆片段的部分组成，在这方面它们在很大程度上是同源的。通过DNA测序，在这个杂交片段倒位时，交叉位点可以定位在Mu反向重复序列对称中心的ACCT序列中。杂交的Mu-P1片段倒位频率低于其亲本可逆片段，这可能是因为Mu和P1的反向重复序列之间存在错配。这表明反向重复序列之间的碱基配对是重组的中间步骤。缺少Mu相邻β区域或P1的亲属P7中相应区域的亚克隆G片段的质粒在倒位方面存在缺陷。通过对Mu DNA进行位点特异性诱变分析，鉴定出一个具有多个识别位点的增强元件，它对于有效倒位是必需的。这个倒位位点的组成部分位于Muβ区域内一个170bp的片段中，在反向重复序列右侧30bp处，但可以通过1200bp的插入与交叉位点分开而不失去其作用。
