HMO2, a yeast HMGB protein that preferentially binds to DNA ends

Abstract

DNA damage is a common hazard that all cells have to combat. Saccharomyces cerevisiae HMO2 is a high mobility group protein (HMGB) that is a component of the chromatin remodeling complex INO80, which is involved in double strand break repair. I show here using DNA end-joining and exonuclease protection assays that HMO2 binds preferentially to DNA ends. While HMO2 binds DNA with both blunt and cohesive ends, the sequence of a single stranded overhang significantly affects binding, supporting the conclusion that HMO2 recognizes features at DNA ends. Analysis of the effect of duplex length on the ability of HMO2 to protect DNA from exonucleolytic cleavage suggests that more than one HMO2 must assemble at each DNA end. HMO2 binds supercoiled DNA with higher affinity than linear DNA and has a preference for DNA with lesions such as pairs of tandem mismatches; however, comparison of DNA constructs of increasing length suggests that HMO2 may not bind stably as a monomer to distorted DNA. The remarkable ability of HMO2 to protect DNA from exonucleolytic cleavage, combined with reports that HMO2 arrives early at DNA double strand breaks, suggests that HMO2 may play a role in double strand break repair beyond INO80 recruitment. I also found that HMO2 has the ability to mediate both 3Œ and 5Œ DNA strand invasion, which is an essential step in homologous recombination. Also hmo2∆ and hmo2∆rad52∆ have slower growth phenotype in presence of hydroxyurea thus indicating that HMO2 might play important role in recovery of stalled DNA replication forks.