FIG. 4.

Amounts of the cspA and cspB mRNAs before and after the cold shock at 15°C, in the presence and in the absence of tryptophan and leucine. E. coli SB221 cells were washed twice at 37°C with M9 medium lacking tryptophan and leucine, and after 10 min the culture was shifted to 15°C. Total RNA was extracted at 37°C before (time zero) and after 10 min of Trp and Leu starvation; at 30, 60, and 120 min in the presence of Trp and Leu; and at 20, 40, 60, and 120 min in the absence of Trp and Leu. Primer extension was carried out for cspA mRNA (a) and cspB mRNA (b) as described previously (3).