Cleavage of holliday junctions by the Escherichia coli RuvABC complex

The Escherichia coli RuvABC proteins process recombination intermediates during genetic recombination and recombinational repair. Although early biochemical studies indicated distinct RuvAB-mediated branch migration and RuvC-mediated Holliday junction resolution reactions, more recent studies have shown that the three proteins act together as a "resolvasome" complex. In this work we have used recombination intermediates made by RecA to determine whether the RuvAB proteins affect the sequence specificity of the RuvC resolvase. We find that RuvAB proteins do not alter significantly the site specificity of RuvC-dependent cleavage, although under certain conditions, they do affect the efficiency of cleavage at particular sites. The presence of RecA also influences cleavage at some sites. We also show that the RuvAB proteins act upon transient strand exchange intermediates made using substrates that have the opposite polarity of those preferred by RecA. Together, our results allow us to develop further a model for the recombinational repair of DNA lesions that lead to the formation of post-replication gaps during DNA replication. The novel features of this model are as follows: (i) the RuvABC resolvasome recognizes joints made by RecA; (ii) resolution by RuvABC occurs at specific sites containing the RuvC consensus cleavage sequence 5'-(A/T)TT downward arrow(G/C)-3'; and (iii) Holliday junction resolution often occurs close to the initiating gap without significant heteroduplex DNA formation.