Nuclease that specifically degrades the RNA of RNA-DNA hybrids. Endonucleolytically removes RNA primers from the Okazaki fragments of lagging strand synthesis on its own. In the presence of Mn(2+) or Co(2+) can also cleave an RNA-RNA hybrid; the dsRNase activity is 10- 100-fold lower than RNase H activity. Complements the temperature-sensitive phenotype of an E.coli double rnhA/rnhB (RNase H) disruption mutant. Endonucleolytic cleavage to 5'-phosphomonoester. Divalent metal cations; Mn(2+) and Mg(2+) are preferred over Co(2+) or Ni(2+). Monomer. The disulfide bond confers considerable stability to the protein. The protein is hyperthermostable, melting temperature (TM) for wild-type is 102 degrees Celsius, for the double Cys mutant is 93 degrees Celsius and for a C-terminal deletion of 6 residues is 77 degrees Celsius.