FIG. 1.

(A) Processing of the rRNA transcript, showing removal of IVSs. A typical 30S rRNA transcribed from an rrn operon is shown with 16S, spacer tRNA, 23S, and 5S rRNAs. The positions of helix 25 IVS (H25) at bp 550 and helix 45 IVS (H45) at bp 1170 are also shown as stem-loop structures on the 23S rRNA. The arrows indicate sites of cleavage by RNase III (an enzyme responsible for primary processing of the nascent 30S rRNA in E. coli and S. enterica serovar Typhimurium). (B) rrl gene for 23S rRNA, indicating positions of helix 25 (about bp 550) and helix 45 (about bp 1170). Also indicated are primers used for PCR amplification of the helix 25 region (P1 and P2) and the helix 45 region (P3 and P4). The rRNA fragmentation patterns expected from excision of IVSs are also shown. The presence of 2.4- and 0.5-kb fragments indicates that an rrl gene contains an IVS in helix 25 only, 1.7 and 1.2-kb fragments indicate an IVS in helix 45 only, and 1.7-, 0.7-, and 0.5-kb fragments indicate IVSs in both helices. Mature 23S rRNA that lacks IVSs is 2.9 kb.