Escherichia coli DNA helicase II (uvrD gene product) catalyzes the unwinding of DNA.RNA hybrids in vitro.

DNA helicase II is a well-characterized Escherichia coli enzyme capable of unwinding duplex DNA and known to be involved in both methyl-directed mismatch repair and excision repair of pyrimidine dimers. Here it is shown that this enzyme also catalyzes the ATP-dependent unwinding of a DNA.RNA hybrid consisting of a radioactively labeled RNA molecule annealed on M13 single-stranded DNA. The DNA.RNA unwinding reaction required less protein to unwind more base pairs than the corresponding unwinding of duplex DNA. In addition, the rate of unwinding of the DNA.RNA hybrid was more than an order of magnitude faster than unwinding of a DNA partial duplex of similar length. The unwinding of the DNA.RNA hybrid is a property unique to helicase II since helicase I, Rep protein, and helicase IV failed to catalyze the reaction. In light of these results it seems likely that helicase II is involved in some previously unrecognized aspect of nucleic acid metabolism, in addition to its known roles in DNA repair reactions.