Site-specific recombination and circular chromosome segregation

Recombinase binding specificity at the chromosome dimer resolution site dif of Escherichia coli 1 1Edited by I. B. Holland

“…Despite this symmetry, the related XerC and XerD site-speci®c recombinases faithfully recognize the two different halves of these elements . An alignment of some of the better characterized core regions recognized by the Xer recombinases indicates that whereas XerD binding sites are well conserved, XerC binding sites are more variable (Figure 1; Sherratt et al, 1993). In the case of dif, the XerC and XerD binding sites are palindromic at six of 11 positions.…”

“…The sequences of the cer-like sites of ColE2-CA42, ColE2-GEI602, ColE2imm-K317, ColE4-CT9, ColE5-099, ColE6-CT14, ColE7-K317, ColE8-J and ColE9-J were described by Hiraga et al (1994). The sequences of other sites are derived from Sherratt et al (1993). bases in the XerD binding site (positions 13, 11 and 10, respectively) among the recombination sites shown in Figure 1 suggesting that these nucleotides may be of particular signi®cance in determining binding speci®city. The relative contributions of these ®ve positions to XerC and XerD binding speci®city was probed using a set of mutated dif sites in which the XerC binding site was made progressively more palindromic with the XerD binding site (see Figure 5A).…”

“…Multimer resolution, active partition, and post-segregational cell killing systems assist either individually or cooperatively in the stabilization of both circular plasmids and the chromosome itself (Hiraga, 1992(Hiraga, , 1993Jensen & Gerdes, 1995;Nordstro È m & Austin, 1989;Sherratt et al, 1993;Wake & Errington, 1995). The Xer sitespeci®c recombination system of Escherichia coli optimizes the number of plasmids available for distribution at cell division by resolving plasmid multimers generated by homologous recombination.…”

Binding and cleavage of nicked substrates by site-specific recombinases XerC and XerD 1 1Edited by M. Yaniv

“…Using a synthetic Holliday junction containing the cer6 site, XerC has been shown to cleave the phosphodiester between the last base of the XerC binding site and the first base of the central region on the top strand (Arciszewska & Sherratt, 1995). To determine directly the cleavage positions for both recombinases at dif, we used top and bottom linear suicide substrates that were labelled at the 3'-end of the central region nick; subsequent reaction with XerC and XerD should release a short oligonucleotide containing the 32 P label, the size of which depends on the cleavage position.…”

“…XerC has also been shown to mediate top strand exchange on cer6 synthetic Holliday junctions, but no bottom strand cleavage or exchange was detected on this substrate. XerC strand exchange occurs at the position of XerC-mediated cleavage (Arciszewska & Sherratt, 1995;Arciszewska et al, 1995).…”