ESCHERICHIA-COLI RNASE-III (RNC) AUTOREGULATION OCCURS INDEPENDENTLY OF RNC GENE TRANSLATION

Control of mRNA stability is an established means of regulating gene e xpression. However, the detailed mechanisms by which such control is a chieved are only now emerging, In particular, there remains a question about the involvement of translation. Escherichia coil ribonuclease I II (RNase III) negatively autoregulates expression of its own gene (me ) approximately 10-fold, by cleaving the untranslated leader and initi ating approximately 10-fold more rapid decay of the me mRNA, after whi ch RNase III plays no further role, Here, we define the mechanism of t his control further, Mutations that increase me gene translation aboli sh autoregulation by increasing the stability of the RNase III-cleaved transcript RNA approximately 10-fold, with no effect on the uncleaved species, Mutations that decrease translation destabilize the me mRNA in the presence or absence of RNase III. In so doing, they reveal a pa thway of me transcript decay distinct from the RNase III-dependent pat hway, Stability of a 'mini-rnc' transcript containing the me leader an d only the first two codons of the me gene is unaffected by decreased translation, presumably because sequences required for this pathway we re removed, Importantly, this mini-me transcript is regulated normally by RNase III, Moreover, me transcripts synthesized in vitro do not de cay in cell-free extracts lacking ribosomes, unless they are first cle aved by RNase III, These two results show that RNase III cleavage can initiate me transcript decay independently of me gene translation, una mbiguously establishing that control of mRNA decay need not involve ch anges in translation, How me gene translation is optimized for efficie nt autoregulation will also be discussed.