The gene encoding a bacterial type 1 RNase H, termed RBD-RNase HI, was cloned from the psychrotrophic bacteriumShewanellasp. SIB1, over-produced inEscherichia coli, and the recombinant protein was purified and biochemically characterized. SIB1 RBD-RNase HI consists of 262 amino acid residues and shows amino acid sequence identities of 26% to SIB1 RNase HI, 17% toE. coliRNase HI, and 32% to human RNase H1.