Abstract

There are many potential mutational threats to the integrity of DNA and multiple DNA repair systems to counteract these. MutS, MutL and MutH are integral elements of dam -directed repair (MMR), a mismatch recognition system involved in rectifying DNA replication errors. Moreover, MutS and MutL have been implicated in the effective endonucleolytic functioning of Vsr, primary player of very short patch (VSP) repair. This study made use of the bacterial two hybrid system in an attempt to further clarify the critical role that each of the above-mentioned proteins plays relative to one another. Our initial goal was to determine specific interactions involved in the MMR pathway. Of the six positive candidates first revealed, four known interactions were observed. A novel liaison between MutS and MutH was detected while binding of MutL to Vsr established a direct link between MMR and VSP repair. The disappearance of the MutS-MutH complex in a mutL background makes a strong case for the role of MutL as a molecular matchmaker. The presence of Vsr impeded proper function of MMR as demonstrated by the lack of MutL homodimerization as well as the disappearance of all interactions involving MutL. This evidence lends further credence to MutL's role as coordinator of MMR and VSP repair.