FIGURE 5.

CroS_R391 regulation of RumAB_R391‐dependent mutagenesis is dependent on the rumAB _R391 promoter region. (a) Spontaneous histidine reversion mutagenesis assays utilizing MVG114 strains harboring pJM1467 (−/−), a pCC1 derivative carrying the rumAB _R391 operon under the control of the recA promoter, were transformed with low‐copy pGB2 derivatives (pJM1365, pJM1366, pJM1367, and pJM1368) carrying various iterations of the croS _R391‐setR _R391 operon (Table 1). The genotypes of croS _R391 or setR _R391, either wild‐type or deleted, are indicated. The histogram illustrates the mean colony count for each indicated strain (n = 5). Error bars represent the standard error of the mean (SEM). An unpaired two‐tailed t test was used to compare the mean colony counts for the ΔsetR ΔcroS and the ΔsetR croS ⁺ strains. * = p < .05. (b) Western blot using an anti‐RumA antibody indicating that the level of RumA expressed from the E. coli recA promoter does not change appreciably in the presence, or absence, of SetR or CroS. Numbers reported for the expression levels of RumA and RumA′ are relative to RumA in the left‐hand lane