Extension of the primers in complexes Tp1:PrI (Series A) and Tp1:PrII (Series B) catalyzed by AMV reverse transcriptase. Series A: lane 1, primer (control); lane 2, primer + enzyme (control); lanes 3–5, as in lane 2 + 10 µM dTTP (3), dTTP + dGTP (4) and dTTP + dGTP + dATP (5); lane 6, as in 2 + 10 µM ddTTP; lane 7, as 2 + 10 µM d4TTP. Series B: lane 1, primer (control); lane 2, primer + enzyme (control); lanes 3–5, as in lane 2 + 200 µM dTTP (3), dTTP + dGTP (4) and dTTP + dGTP + dATP (5); lanes 6 and 7, as in 2 + 10 µM (6) and 100 µM (7) ddTTP; lanes 8 and 9, as in 2 + 10 (8) and 100 µM (9) d4TTP, respectively.