THE ENDORIBONUCLEOLYTIC N-TERMINAL HALF OF ESCHERICHIA-COLI RNASE-E IS EVOLUTIONARILY CONSERVED IN SYNECHOCYSTIS SP. AND OTHER BACTERIA BUTNOT THE C-TERMINAL HALF, WHICH IS SUFFICIENT FOR DEGRADOSOME ASSEMBLY

Escherichia coli RNase E, an essential single-stranded specific endori bonuclease, is required for both ribosomal RNA processing and the rapi d degradation of mRNA, The availability of the complete sequences of a number of bacterial genomes prompted us to assess the evolutionarily conservation of bacterial RNase E, We show here that the sequence of t he N-terminal endoribonucleolytic domain of RNase E is evolutionarily conserved in Synechocystis sp. and other bacteria. Furthermore, we dem onstrate that the Synechocystis sp, homologue binds RNase E substrates and cleaves them at the same position as the E. coli enzyme. Taken to gether these results suggest that RNase E-mediated mechanisms of RNA d ecay are not confined to E, coli and its close relatives. We also show that the C-terminal half of E. coli RNase E is both sufficient and ne cessary for its physical interaction with the 3'-5' exoribonuclease po lynucleotide phosphorylase, the RhlB helicase, and the glycolytic enzy me enolase, which are components of a ''degradosome'' complex. Interes tingly, however, the sequence of the C-terminal half of E, coli RNase E is not highly conserved evolutionarily, suggesting diversity of RNas e E interactions with other RNA decay components in different organism s. This notion is supported by our finding that the Synechocystis sp, RNase E homologue does not function as a platform for assembly off. co li degradosome components.