Table 1. Pre-steady-state kinetic constants for dNTP and rNTP incorporation by wild-type and F12A Dbh^a.

Protein/DNA	Kd (mM)	kpol (s–1)	kpol/Kd	Kd (mM)	kpol (s–1)	kpol/Kd	Selectivityb
DNA duplex A (non-frameshift)	5′-TCGAAGCGACGGG
	3′-AGCTTCGCTGCCCCTTTCCATCA
	dGTP			rGTP			dG/rG
Wild-type	0.37 ± 0.19	(2.3 ± 0.9) × 10–2	62	0.77 ± 0.36	(1.4 ± 0.3) × 10–5	1.8 × 10–2	3400
F12A	0.95 ± 0.1	(2.1 ± 0.5) × 10–3	2.2	1.3 ± 0.2	(7.8 ± 1.4) × 10–4	0.6	3.7
DNA duplex B (frameshift)	5′-GCATTTTCTGCTCCGG
	3′-CGTAAAAGACGAGGCCCGCC
	dCTP			rCTP			dC/rC
Wild-type	0.46 ± 0.21	(1.9 ± 1.1) × 10–2	41	0.58 ± 0.49	(3.1 ± 2.9) × 10–6	5.3 × 10–3	7700
F12A	1.6 ± 0.6	(4.0 ± 2.0) × 10–4	0.25	3.3 ± 1.0	(1.6 ± 0.5) × 10–4	0.05	5.0

^aKinetic parameters are the average of at least two independent determinations and are reported as mean ± SD. The relatively large standard deviations in the case of rNTP incorporations by wild-type Dbh are a consequence of the extremely slow rates of these reactions.

^bSelectivity was calculated as the ratio of k_pol/K_d values (dNTP/rNTP).