The Endoribonucleolytic N-Terminal Half Of Escherichia Coli Rnase E Is Evolutionarily Conserved In Synechocystis Sp. And Other Bacteria But Not The C-Terminal Half, Which Is Sufficient For Degradosome Assembly

Escherichia coli RNase E, an essential single-stranded specific endoribonuclease, is required for both ribosomal RNA processing and the rapid 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 the N-terminal endoribonucleolytic domain of RNase E is evolutionarily conserved in Synechocystis sp. and other bacteria. Furthermore, we demonstrate that the Synechocystis sp, homologue binds RNase E substrates and cleaves them at the same position as the E. coli enzyme. Taken together these results suggest that RNase E-mediated mechanisms of RNA decay 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 necessary for its physical interaction with the 3'-5' exoribonuclease polynucleotide phosphorylase, the RhlB helicase, and the glycolytic enzyme enolase, which are components of a "degradosome" complex. Interestingly, however, the sequence of the C-terminal half of E, coli RNase E is not highly conserved evolutionarily, suggesting diversity of RNase E interactions with other RNA decay components in different organisms. This notion is supported by our finding that the Synechocystis sp, RNase E homologue does not function as a platform for assembly off. coli degradosome components.