Evidence of RNA in D loops of intracellular lambda DNA.

If lambda DNA replication is blocked by mutation in any one of several genes essential for replication, intracellular lambda DNA often shows short three-stranded regions called D loops. In this report we show that one arm of a D loop is an RNA . DNA hybrid, whereas the remaining arm is made up of single-stranded DNA. The RNA can be partially removed by RNase A and totally removed by RNase H. Also, D loops do not appear if infections are made in cells treated with rifampin, a potent inhibitor of transcription by Escherichia coli RNA polymerase. Several genes associated with recombination, including the host recA gene, are not essential for D-loop formation.