FIGURE 4.
RNase II protects more efficiently the rpsO mRNA from RNase R-mediated degradation if incubation at high temperature is short. To inactivate the thermosensitive RNase Ets, cell cultures were grown at 30°C and shifted to 44°C with immediate addition of rifampicin to blockage of transcription, and samples were withdrawn at times indicated. Total RNA from cells carrying both (rne-1), only one (rne-1 rnr and rne-1 Δrnb), or any (rne-1 Δrnb rnr) of the hydrolytic exonucleases RNase II and RNase R were analyzed on 6% polyacrylamide Northern blots. rpsO mRNA was detected using an antisense riboprobe. P1-t1 corresponds to the monocistronic rpsO transcript while the P1-RIII results from the processing of the rpsO-pnp bicistronic transcript.