Primer extension by compounds IIIa–d catalyzed by TDTP– (Series A, lanes 1–14) and TDTP+ (Series A, lanes 15–20, Series B, lanes 1–4). (A) Lane 1, primer + enzyme (control); lane 2, as in lane 1 + 0.5 µM ddTTP; lanes 3–6, as in lane 1 + 2.5, 10, 25 and 100 µM IIIa, respectively; lanes 7–10, as in lane 1 + 2.5, 10, 25 and 100 µM IIIb, respectively; lanes 11–14, as in lane 1 + 0.025, 0.1, 0.25 and 1 µM IIId, respectively; lanes 15–17, as in lane 1 + 0.01, 0.1 and 1 µM IIId, respectively; lanes 18–20, as in lane 1 + 1, 10 and 100 µM IIIc, respectively. (B) Lane 1, primer + enzyme (control); lane 2, as in lane 1 + 0.2 µM ddTTP; lane 3, as in lane 1 + 5 µM IIId; lane 4, 3′-phosphorylated 14mer oligodeoxynucleotide VII.