EMBO J. 1997 Feb 17;16(4):856-65 doi:10.1093/emboj/16.4.856

Kulpa D, Topping R, Telesnitsky A.

Determination of the site of first strand transfer during Moloney murine leukemia virus reverse transcription and identification of strand transfer-associated reverse transcriptase errors.

“The results presented here support the model that +1 substitutions arise during reverse transcription via non‐templated addition followed by mismatch extension upon strand transfer. Another possibility we considered was that +1G could potentially be templated by the 7‐methyl‐G cap present on mRNAs and viral genomic RNAs (Coffin, 1996). Avian myeloblastosis virus reverse transcriptase can add a cap‐complementary C residue during cDNA synthesis on mRNA in vitro, but not when the RNA has been de‐capped (Volloch et al., 1995). However, studies with purified enzymes and model primer–templates have demonstrated that +1G can arise at template switch junctions in the absence of a 7‐methyl‐G cap (Peliska and Benkovic, 1994), and our detection of +1C mutants demonstrates that not all additions to −ssDNA could be cap‐templated.”