hMSH4-hMSH5 adenosine nucleotide processing and interactions with homologous recombination machinery

We have previously demonstrated that the human heterodimeric meiosis-specific MutS homologs, hMSH4-hMSH5, bind uniquely to a Holliday Junction and its developmental progenitor (Snowden, T., Acharya, S., Butz, C., Berardini, M., and Fishel, R. (2004) Mol. Cell 15, 437-451). ATP binding by hMSH4-hMSH5 resulted in the formation of a sliding clamp that dissociated from the Holliday Junction crossover region embracing two duplex DNA arms. The loading of multiple hMSH4-hMSH5 sliding clamps was anticipated to stabilize the interaction between parental chromosomes during meiosis double-stranded break repair. Here we have identified the interaction region between the individual subunits of hMSH4-hMSH5 that are likely involved in clamp formation and show that each subunit of the heterodimer binds ATP. We have determined that ADP-->ATP exchange is uniquely provoked by Holliday Junction recognition. Moreover, the hydrolysis of ATP by hMSH4-hMSH5 appears to occur after the complex transits the open ends of model Holliday Junction oligonucleotides. Finally, we have identified several components of the double-stranded break repair machinery that strongly interact with hMSH4-hMSH5. These results further underline the function(s) and interactors of hMSH4-hMSH5 that ensure accurate chromosomal repair and segregation during meiosis.