Short-patch reverse transcription in Escherichia coli.

Chimeras of RNA and DNA have distinctive physical and biological properties. Chimeric oligonucleotides that contained one, two or three ribonucleotides whose phosphodiester backbone was covalently continuous with DNA were synthesized. Site-directed mutagenesis was used to assess genetic information transfer from the ribonucleotide positions. Transfer was scored by the formation or reversion of an ochre site that also corresponded to a restriction cleavage site. This allowed physical as well as genetic assay of mutational events. Bases attached to the ribonucleotides were able to accurately direct the synthesis of progeny DNA. The results suggest that in vivo DNA polymerases utilize a "running start" on a DNA backbone to continue across a covalent backbone junction into a region of ribonucleotides and then back again onto a normal DNA backbone. The phenomenon is designated short-patch reverse transcription (SPRT) by analogy to short-patch mismatch correction and reverse transcription as the term is generally used. The possibility is considered that SPRT contributes to an unrecognized pathway of mutagenesis.