TABLE 4.

Growth rate in minimal medium of strains mutated in a Walker motif and lacking RNase R

Overnight cultures of the same strains as in Table 3 were subcultured into M9/glucose minimal medium and grown measured at the indicated temperatures. Periodic measurements of A₆₀₀ were made within the exponential growth phase. Cell doubling times and standard deviations were calculated based on data from five replicate experiments. RA and RB indicate the R736A and the D168A,D169A Walker A and Walker B mutants, respectively. Data for the R⁻ column were repeated from Table 2 for comparison purpose. * denotes p < 0.0001 by a two-tailed Student's t test as compared with the PNP⁻ strain.

Growth temperature	Doubling time (min)
	R −	PNP−	PNP− RA	PNP− RB
42 °C	81 ± 6	84 ± 5	142 ± 6*	136 ± 6*
37 °C	65 ± 5	67 ± 5	153 ± 7*	149 ± 6*
31 °C	126 ± 6	135 ± 7	No growth	No growth
25 °C	183 ± 7	202 ± 8	No growth	No growth