Function in Escherichia coli of the non-catalytic part of RNase E:: role in the degradationof ribosome-free mRNA

RNase E contains a large non-catalytic region that binds RNAand the protein components of the Escherichia coli RNA degradosome.The rne gene was replaced with alleles encoding deletionsin the non-catalytic part of RNase E. All the proteins are stable invivo. RNase E activity was tested using a P-T7-lacZ reportergene, the message of which is particularly sensitive to degradationbecause translation is uncoupled from transcription. The non-catalytic regionhas positive and negative effectors of mRNA degradation. DisruptingRhlB and enolase binding resulted in hypoactivity, whereas disruptingPNPase binding resulted in hyperactivity. Expression of the mutantproteins in vivo anticorrelates with activity showing thatautoregulation compensates for defective function. There is no simplecorrelation between RNA binding and activity in vivo. Anallele (rne131), expressing the catalytic domain alone, wasput under P (lac) control. In contrast to rne (+),low expression of rne131 severely affects growth. Even withautoregulation, all the mutants are less fit when grown in competitionwith wild type. Although the catalytic domain of RNase E is sufficientfor viability, our work demonstrates that elements in the non-catalyticpart are necessary for normal activity in vivo.