FIG. 2.

(A) rRNA from bacterial strains, detected by electrophoresis, Northern blotting, and methylene blue staining. The same seven strains were tested, in the same order, as in Fig. 1. See Table 1 for a list of the strains tested. Normal rRNA sizes are indicated on the right (23S and 16S). Sizes, in kilobases, on the left indicate fragmented rRNA. (B) The heavy line at the top indicates the full-length rrl gene for 23S rRNA; when transcribed, this produces rRNA of 2.9 kb. The boxes at helix 25 and helix 45 indicate IVSs which result in posttranscriptional cleavage of the rRNA by RNase III. 23S rRNA fragments of 2.4 and 0.5 kb indicate that one rrl gene carries an IVS in helix 25. 23S rRNA fragments of 1.7 and 1.2 kb indicate that one rrl gene carries an IVS in helix 45. 23S rRNA fragments of 1.7, 0.7, and 0.5 kb indicate that one rrl gene carries IVSs in both helices. See the text for an interpretation of the number of rrl genes with IVSs in each strain.