The effects of internal primer-template mismatches on RT-PCR: HIV-1 model studies.

We investigated the effects of internal primer-template mismatches on the efficiency of reverse transcription and PCR amplification. As models, RNA transcripts representative of different HIV-1 group M subtypes were evaluated with a previously described gag primer pair system. We observed that the presence of two to four mismatches in the primer-template duplexes did not have a significant effect on RT-PCR. However, the presence of five and six mismatches with the 28 and 30 base primers reduced PCR product yield by approximately 22- and 100-fold respectively, relative to the homologous template. The amount of reduction was reproducible from experiment to experiment and was independent of the initial copy number input. Under the conditions used, viral RNA measurements of the more divergent HIV-1 subtypes (A and E) would be underestimated, while isolates of subtypes B, C, D and F-H are expected to be efficiently amplified and accurately measured. The reduced amplification efficiency for targets similar to HIV subtypes A and E can be improved 4- to 10-fold by lowering the annealing temperature and implementing a reverse transcription step that gradually increases in temperature. The additional substitution of either 5-methylcytosine for cytosine throughout or the substitution of inosine at positions of variable bases resulted in a <4-fold difference in product yield between the homologous and most divergent templates.