FIG. 2.

Timing of ritR mRNA synthesis during the growth of S. pneumoniae. A culture of S. pneumoniae CPU401 containing a promoterless E. coli LacZ reporter inserted into the ritR open reading frame was sampled as indicated for determination of turbidity, measured at 600 nm (A600), and for determination of E. coli LacZ activity, measured fluorimetrically at 480 nm (F480) with methylumbelliferyl galactoside as a LacZ substrate. The normalized specific activity of LacZ is plotted as F480/A600. The ritR promoter activity reached the maximal value during exponential growth and decreased as cells entered the stationary phase. To purify RNA for microarray studies, cells were harvested at an A₆₀₀ of 0.4, as indicated by the arrow, which corresponded to the time at which the ritR mRNA initially reached the maximum level.