PARAMETERS THAT INFLUENCE PROCESSIVE SYNTHESIS AND SITE-SPECIFIC TERMINATION BY HUMAN-IMMUNODEFICIENCY-VIRUS REVERSE-TRANSCRIPTASE ON RNA AND DNA TEMPLATES

We have examined the parameters that determine the length and distribution of products synthesized processively by the human immunodeficiency virus reverse transcriptase (HIV-RT). On native or homopolymer templates, the overall length distribution of processively synthesized products is increased by increased temperature or deoxynucleoside triphosphate concentration, or decreased ionic strength. Specific terminations of processive synthesis on either native DNA or RNA templates occur most frequently at positions where the reverse transcriptase (RT) pauses during synthesis. These sites correlate with the template sequence 3'-(A/U)(A/U)(G/C)-5', particularly when this sequence is predicted to be base paired with another region of the template in a secondary structure. Many positions of termination are in similar positions on DNA or RNA templates. Notable exceptions are runs of A residues, which promote termination on DNA but not RNA templates. Termination intensities vary when different RTs are used demonstrating an influence of RT structure.