FIG. 3.

Timing of RNAIII, α-hemolysin (hla) and serine protease (spr) gene transcription. Cultures were started in early exponential phase (5 × 10⁷ cells/ml), and samples were removed at hourly intervals for determination of cell density and for preparation of whole-cell RNA for Northern hybridization analysis. The amount of RNA in each sample was normalized to that of the rRNA, which was quantitated by scanning an ethidium bromide-stained agarose gel with an Alpha-Inotech video-imager. (A) Growth curves of RN4850 and RN7690. Cell densities (optical densities [OD]) were measured with a Molecular Devices microplate reader at 650 nm. (B and C) Northern hybridization analysis using a probe specific for RNAIII, hla, or spr. The arrow indicates the full-sized transcript containing the gene.