Structure of Bacteriophage T4 RNase H, a 5′ to 3′ RNA–DNA and DNA–DNA Exonuclease with Sequence Similarity to the RAD2 Family of Eukaryotic Proteins

Abstract

Bacteriophage T4 RNase H is a 5′ to 3′ exonuclease that removes RNA primer from the lagging strand of the DNA replication fork and is a member of the RAD2 family of eukaryotic and prokaryotic replication and repair nucleases. The crystal structure of the full-length native form of T4 RNase H has been solved at 2.06 Å resolution in the presence of Mg 2+ but in the absence of nucleic acids. The most conserved residues are clustered together in a large cleft with two Mg 2+ in the proposed active site. This structure suggests the way in which the widely separated conserved regions in the larger nucleotide excision repair proteins, such as human XPG, could assemble into a structure like that of the smaller replication nucleases.