Inefficient repair of-RNA · DNA hybrids

RNA · DNA hybrids are commonly observed during normal biological processes. We tested the ability of three DNA-repair enzymes to remove lesions from the DNA strand of RNA · DNA heteroduplexes. Three nucleotide analogs, 5-hydroxy-2'-deoxycytidine triphosphate, 8-oxo-2'-deoxyguanosine triphosphate, and O⁶-methyl-2'-deoxyguanosine triphosphate, representative of lesions generated by oxygen damage and methylating agents, were incorporated into the DNA strand synthesized using either a DNA or RNA template. The extended DNA · DNA and RNA · DNA hybrids were used as substrates for bacterial formamidopyrimidine-DNA glycosylase, Nth protein (endonuclease III) and O⁶-methylguanine-DNA methyltransferase. We show that all three lesions are readily cleaved from the DNA strand of a DNA · DNA duplex but are relatively resistant to cleavage when present in the DNA strand of an RNA DNA hybrid. Our in vitro studies suggest that damaged DNA in RNA · DNA hybrids is less likely to be repaired in vivo.