RNASE-E AUTOREGULATES ITS SYNTHESIS BY CONTROLLING THE DEGRADATION RATE OF ITS OWN MESSENGER-RNA IN ESCHERICHIA-COLI - UNUSUAL SENSITIVITY OF THE RNE TRANSCRIPT TO RNASE-E ACTIVITY

RNase E is a key regulatory enzyme that appears to control the principal pathway for mRNA degradation in Escherichia coli. Here, we show that RNase E represses its own synthesis by reducing the cellular concentration of the me (RNase E) gene transcript. Autoregulation is achieved by modulating the longevity of this 3.6-kb mRNA, whose half-life ranges from <40 sec to >8 min depending on the level of RNase E activity in the cell. feedback regulation is mediated in cis by the 5'-terminal 0.44-kb segment of me mRNA, which is sufficient to confer this property onto a heterologous transcript to which it is fused. Like the intact protein, an amino-terminal fragment of RNase E lacking 563 amino acid residues can act in trans to repress me gene expression. Paradoxically, raising the me gene copy number 21-fold in E. coIi causes an unexpected reduction in the concentration of the full-length me transcript, yet results in a small increase in RNase E protein production These surprising phenomena are explained in terms of a model in which the degradation of this long and highly labile mRNA commences before elongation of the nascent transcript has been completed. In such circumstances, gene expression can be unusually sensitive to changes in mRNA stability.