Misincorporation by AMV reverse transcriptase shows strong dependence on the combination of template and substrate nucleotides.

We have carried out a systematic investigation of the efficiency of misincorporation by Avian Myeloblastosis Virus reverse transcriptase with all possible combinations of dNTP substrate, template nucleotide, and the nucleotide at the 3' terminus of the primer. A series of synthetic oligonucleotide primers were annealed to single stranded M13 DNA templates, and a single dNTP was misincorporated at the primer 3' end using AMV reverse transcriptase. The proportion and pattern of misincorporation and incorporation in all 64 situations was assayed using [5'-32p] labelled primers, and the products were separated on denaturing polyacrylamide gels. Correct incorporations occurred more readily than misincorporations. The efficiency of misincorporation depended on the individual primer, but, comparing primers, a clear dependence on the template nucleotide was observed for the preferential misincorporation of different dNTPs. The exact combination of template and dNTP was important; although purine:pyrimidine (dNTP substrate:template nucleotide) and pyrimidine:purine misincorporations occurred comparatively readily, some pyrimidine:pyrimidine and purine:purine reactions were equally efficient and yet others were never seen to occur. Some misincorporations were facilitated by subsequent correct incorporations, but despite this our results suggest that the level of misincorporation is limited by the rate of reaction and enzyme inactivation rather than by exonuclease activity.