Autoregulation allows Escherichia coli RNase E to adjust continuously its synthesis to that of its substrates

The Escherichia coli endonuclease RNase E plays a key role in rRNA maturati on and mRNA decay. In particular, it controls the decay of its own mRNA by cleaving it within the 5'-untranslated region (UTR), thereby autoregulating its synthesis. Here, we report that, when the synthesis of an RNase E subs trate is artificially induced to high levels in vivo, both the me mRNA conc entration and RNase E synthesis increase abruptly and then decrease to a st eady-state level that remains higher than in the absence of induction. Usin g rne-lacZ fusions that retain or lack the me 5'UTR, we show that these var iations reflect a transient mRNA stabilization mediated by the me 5'UTR. Fi nally, by putting RNase E synthesis under the control of an IPTG-controlled promoter, we show that a similar, rne 5'UTR-mediated mRNA stabilization ca n result from a shortage of RNase E. We conclude that the burst in substrat e synthesis has titrated RNase E, stabilizing the me mRNA by protecting its 5'UTR. However, this stabilization is self-correcting, because it allows t he RNase E pool to expand until its mRNA is destabilized again. Thus, autor egulation allows RNase E to adjust its synthesis to that of its substrates, a behaviour that may be common among autoregulated proteins. Incidentally, this adjustment cannot occur when translation is blocked, and we argue tha t the global mRNA stabilization observed under these conditions originates in part from this defect.