TABLE 4.

RhuI competes with ς^S for binding to E. coli RNA polymerase^a

Plasmid	RhuI expression	β-Galactosidase activity (Miller units)b
		−IPTG	+IPTG
pRK415	−	109.2 (3.9)	100.3 (3.9)
pERM26	+	114.0 (4.9)	86.7 (1.6)*

^aPlasmids were transformed into E. coli AF633 which contains a lacZYA reporter operon under the control of the ς^S-dependent uspB promoter (11). Expression of a sigma factor other than ς^S in this strain results in a decreased expression of the LacZ reporter. All plasmids were cotransformed with placI as a source of the LacI^q1 repressor. Cells were induced for RhuI expression by the addition of IPTG to a final concentration 0.1 mM at the time of inoculation. 

^bReporter activity was determined by a modified version of the Miller assay (2, 27). The mean and standard deviation (in parentheses) are shown for each value. The asterisk indicates that the value is significantly different from the value for the uninduced control (P < 0.05), as determined by the Student t test.