Structural basis for the interaction between E. coli RNase HI and SSB

Abstract

Single‐strand (ss) DNA binding proteins (SSBs) interact with over a dozen different DNA replication, recombination, and repair proteins in bacterial cells. These interactions help drive genome maintenance processes by recruiting diverse enzymatic activities to their cellular sites of action. We have identified a new interaction between SSB and Ribonuclease HI (RNase HI) from E. coli that we hypothesize is important for targeting the nuclease to the RNA primers on the lagging strand during DNA replication. SSB stimulates RNase HI activity (hydrolysis of RNA in RNA/DNA hybrids) in vitro, possibly through recruitment of the enzyme to hybrids that are adjacent to SSB/ssDNA. We have shown that RNase HI binds to the C‐terminus of SSB (SSB‐Ct), which is a mode of interaction that is shared among all SSB interaction partners examined to date. Crystallographic and NMR studies coupled with isothermal titration calorimetry have mapped the SSB‐binding site on RNase HI. Future work is aimed at testing the hypothesis that the SSB/RNase HI interaction targets RNase HI to the lagging strand in vivo. Research supported by GM068061.