TABLE 2.

RNA binding affinities of the proteins^a

Protein	RNAb	K1/2 (without NTP)	K1/2c (with ADP)	K1/2c (with AMP-PNP)
Wild type	R1	180 ± 50	210 ± 30	NDd
Wild type	RNA01	230 ± 20	270 ± 30	35 ± 12
Wild type	RNA02	200 ± 50	290 ± 60	40 ± 14
F405A	R1	890 ± 180	1000 ± 200	860 ± 200
F405A	RNA01	ND	ND	700 ± 70
F405L	R1	250 ± 30	220 ± 40	120 ± 20
F405M	R1	ND	ND	53 ± 5

^aThe K_1/2s (half saturation values) were derived from the best fit of the data to the equation θ = nK[L]^m/(1 + K[L]^m), where θ is the fraction of RNA bound, n is the number of binding sites, [L] is the ligand concentration, K is the binding constant, and m is the Hill coefficient. Best fits were obtained with either n = 1 or n as a variable (always approximately 1). A minimum of 10% error was assumed in the protein concentrations; larger errors are the standard deviations from the means of three or more independent experiments.

^bRNA substrates were 44-mer R1 (5′ GGGCGAAUUCAAAACAAAACAAAACUAGCACCGUAAAGCAAGCU 3′), 25-mer RNA01 (5′ UCAUACUUUUCUUUUCUUUUCCAUC 3′), or 25-mer RNA02 (5′ GAUGGAAAAGAAAAGAAAAGUAUGA 3′).

^cADP and AMP-PNP concentrations were 5 mM.

^dND, not determined.