Figure 4.

Accumulation of the rRNA precursors and aberrant ribosomal subunits. (A) The ratios of the 5′-end counts and 3′-end counts of the mature- and precursor rRNA ends. Comparison of the PNK+ toxin induction (MazF, MqsR) and wt stationary phase libraries to the no toxin control. (B) Sucrose density gradient centrifugation profiles of the no toxin control and the cultures after 2 hours of induction of either MqsR or MazF. Peaks of irregular subunits (*50S, *30S, and **30S) are marked by asterisks. (C) The irregular ribosomal subunits contain fragmented rRNA. RNA from the sucrose gradient fractions was analyzed by Northern hybridization. RNA (2 µg per lane) was separated on a 1.5% agarose gel, transferred to a membrane, and hybridized with the oligoprobes 16S P1 and 23S P. Total RNA of the MqsR induction culture was used as a control. Bands that occur in all 70S lanes due to the RNA cleavages during ribosome preparation are marked by arrowheads (>).