FIG. 3.

Defects in 23S rRNA maturation caused by a lack of 3′-to-5′ exonucleases. MG1655* or MG1655* Δrph Δrnb Δrnt was grown in LB at 37°C, and RNA was extracted from exponentially growing cultures. 23S rRNA processing was evaluated at the 3′ end (A) or at the 5′ end (B). Lane 1, MG1655*; lane 2, MG1655* Δrph Δrnd Δrnt. The positions of the unprocessed (U) and processed (P) RNAs are indicated. The ratio of unprocessed and processed RNA (U/P) at the 5′ end is also shown in panel B. (C) Kinetics of 5′-end processing. Cultures of MG1655* Δrph Δrnd Δrnt were harvested at the indicated times after rifampin addition, and RNA preparations derived from the cultures were assayed by primer extension. The fraction of unprocessed rRNA versus time after the addition of rifampin is plotted on a semilogarithmic graph. Each point represents the average from three independent experiments. A straight line obtained by linear regression is shown. For comparison purposes, a dashed line that corresponds to 5′-end maturation in a wild-type strain (see Fig. 2D) is also shown.