Table S2.

Kinetic parameters for GTP hydrolysis and peptidyl transfer from ternary complex with T-stem mutated tRNA^Glu

	GAA (Cognate)	GAU				GGA				GAC
Mutants	(kcat/Km)GTP	(kcat/Km)GTP	(kcat/Km)dip	I	F	(kcat/Km)GTP	(kcat/Km)dip	I	F	(kcat/Km)GTP	(kcat/Km)dip	I	F
	(µM-1s-1)	(mM-1s-1)				(mM-1s-1)				(mM-1s-1)
WT	8.1 ± 1.5	132 ± 10	1.26 ± 0.12	61 ± 12	105 ± 13	39 ± 3	0.29 ± 0.03	209 ± 42	133 ± 17	51 ± 3	0.38 ± 0.02	158 ± 31	134 ± 11
T1	5.5 ± 0.5	95 ± 6	1.27 ± 0.07	58 ± 6	75 ± 6	28 ± 2	0.27 ± 0.03	195 ± 20	104 ± 14	39 ± 2	0.43 ± 0.03	142 ± 15	89 ± 8
T2	10.2 ± 1.9	124 ± 25	2.26 ± 0.23	82 ± 22	55 ± 12	36 ± 2	0.60 ± 0.07	284 ± 55	60 ± 8	52 ± 3	0.89 ± 0.14	196 ± 38	59 ± 10
W1	1.2 ± 0.2	30 ± 7	1.56 ± 0.28	40 ± 11	19 ± 5	12 ± 2	0.30 ± 0.03	192 ± 24	39 ± 7	17 ± 2	0.62 ± 0.03	72 ± 16	27 ± 4
W2	2.2 ± 0.5	18 ± 3	1.10 ± 0.08	123 ± 32	17 ± 3	4.4 ± 2.1	0.19 ± 0.04	502 ± 263	23 ± 12	6.6 ± 1.6	0.34 ± 0.03	336 ± 106	19 ± 5

Kinetic efficiency for cognate and near-cognate GTP hydrolysis, (k_cat/K_m)_GTP, were estimated from experiments with ribosomes at 1 and 2 µM, which are always in excess over ternary complex. The rate of GTP hydrolysis at 2 µM was always twice that at 1 µM with virtually identical k_cat/K_m estimates. Kinetic efficiencies for near-cognate dipeptide formation, (k_cat/K_m)_dip, were derived from titrations of ternary complex in excess over ribosomes. Initial selection (I) was calculated from the ratio of cognate to near-cognate (k_cat/K_m)_GTP parameters. Proofreading factor (F) was calculated from the ratio between near-cognate k_cat/K_m-values for GTP hydrolysis and dipeptide formation (see SI Materials and Methods). Data represent weighted averages from at least two independent experiments ± propagated SD.