Table 5.

Polymerase Residues Interacting with Divalent Cation or Sugar

	divalentcation		sugar
polymerase	motif A	motif C	motif A	motif B	ref
3Dpol	Asp-233	Asp-328	Asp-238	Asn-297	3, 4
HIV-RT	Asp-110	Asp-185	Tyr-115	Phe-160	5
T7 RNAP	Asp-537	Asp-812	Gly-542/Tyr-639a	His784	20, 21
T7 DNAP	Asp-475	Asp-654	Glu-480	Gln-615b	22
BF	Asp-653	Asp-830	Glu-658	Gln-797b	19
Klenow	Asp-705	Asp-882	Glu-710	Gln-849b	23, 31
RB69	Asp-411	Asp-623	Tyr-416	Gly-393	30
Taq	Asp-610	Asp-785	Glu-615	Gln-754	24

^aG542 is the structurally analogous residue to Asp-238 of 3D^pol. Tyr-639 is involved in selection for a 2′-OH (28).

^bThese residues are locked in a conformation away from the ribose-binding pocket by the Asp-238 equivalent in these enzymes.