Table 2.

Effects of substitutions in RNAP on reduction of promoter complex half-life by ppGpp.

Substitution (E. coli RNAP numbering)	Relative lifetime without ppGppa	Relative lifetime at saturating ppGppb	Relative IC50 (mutant IC50 / WT IC50)c
wild-type RNAP	1	0.47 ± 0.08	1
β′ Q504E	0.99 ± 0.11	0.48 ± 0.04	1.56 ± 0.20
B′ K598A/K599A	1.14 ± 0.08	0.40 ± 0.08	0.57 ± 0.00
β′ N458S	0.90 ± 0.08	0.40 ± 0.02	0.43 ± 0.13
β′ R731A	1.86 ± 0.12	0.40 ± 0.03	0.25 ± 0.02
β′ E925A	1.68 ± 0.10	0.24 ± 0.05	0.92 ± 0.20
β′ Q929A	1.23 ± 0.10	0.26 ± 0.06	0.46 ± 0.10
β E813A/E814A	0.76 ± 0.02	0.36 ± 0.00	0.60 ± 0.14
β R1106A	0.98 ± 0.10	0.32 ± 0.02	0.52 ± 0.15

^aHalf-lives were measured on the lacUV5 promoter using a filter-binding assay as described in Materials and Methods and Fig. 3 legend. Reported half-lives are from at least two titrations, each including ≥ 5 ppGpp concentrations.

^bThe values reported are the lifetimes of the promoter complexes at saturating ppGpp concentration relative to the same complexes without ppGpp, taken from the plateau values on plots like those illustrated in Fig. 3 and Supplemental Fig. 2. The reported values are from the same experiments as the intrinsic half-lives (i.e. without ppGpp).

^cThe relative IC₅₀ is the concentration of ppGpp resulting in a half-maximal decrease in complex lifetime with the mutant RNAP, relative to that with the wild-type RNAP. The half-lives were taken from plots like those shown in Fig. 3 and Supplemental Fig. 2, representing ≥ 2 determinations at each ppGpp concentration.