TABLE 1.

K_i for His- and GST-His-OBD and IC₅₀ for T antigen^a

Competitor	Ki (nM) for:		IC50 (nM) for T antigen
	His-OBD	GST-His-OBD	−ADP-Mg	+ADP-Mg
0 TBS	>924	>60	>3,875	237
1 TBS	28	4	53	50
2 TBS	48	0.9	60	112
Site II 1234	31	0.5	14	13
Site II mut	>1,550	>33	3,758	75
Site II 1	107	7	47	38
Site II 2	150	11	211	45
Site II 3	57	4	60	21
Site II 4	123	8	159	27
Site II 13	39	0.7	18	28
Site II 24	62	1	56	35
Site II 13+1	50	ND	33	ND
Site II 13+2	58	ND	27	ND
Site II 13+3	80	ND	29	ND
Core	50	0.9	19	1
Core mut	>376	>24	>3,875	15

^aK_i values and IC₅₀ were calculated as indicated in the text from inhibition curves obtained with the indicated competitor duplex DNA in binding reactions performed with the one TBS-containing probe. K_i values for the His-OBD and GST-His-OBD proteins were obtained from binding reactions performed in buffer containing 100 mM NaCl. IC₅₀ for T antigen were obtained from binding reactions containing 50 mM NaCl. The concentrations of proteins and probe were, respectively, 100 and 15 nM for His-OBD, 100 and 15 nM for GST-His-OBD, and 34 and 15 nM for full-length T antigen. When indicated, ADP and Mg were used at concentrations of 4 and 7 mM, respectively (ADP-Mg). Values presented are the average of two independent measurements that typically varied by less than 10% from the mean value. ND, not determined.