The Protein Leves Of RNase E And Other RNases In Anabaena Sp.PCC 7120

Tens of ribonuc leases have been identified in E.coli.One of them,RNase E,serves as the core in RNA degradosome,a proteinaceous complex globally regulating RNA metabolism and playing key roles in cellular growth and enviroment adaptation.Due to the diversity of prokaryotes,the RNA metabolism mediated by ribonucleases could have big difference among various organisms.For instance,the major RNA degradation machinery in Bacillus subtilis is not based on RNase E,but on RNase Y.Currently,most of our knowledge on prokaryotic ribonucleases is from studies on E.coli and B.subtilis.Cyaobacteria are a unique group of ancient and oxygen-evolving phototrophic bacteria.Bioinformatic anylysis reveals that cyanobacterial genomes encode many ribonucleases conserved in most bacteria.How are these cyanobacterial ribonucleases involved in the cellular activities and metabolic processes?Intrigued by this question,we investigated the expression of ribonucleases in the cyanobacterium Anabaena sp.PCC 7120.We made the multiclonal antibodies specifically against eachAnabaena ribonuclease by immuning rabbit with purified recombinant antigen.Using these antibodies,we examined the protein level of each ribonuclease at different growth phases and under nitrogen-depletion conditions.At log phase and stationay phase,the protein levels of all ribonucleases were found to be constant.Upon nitrogen depletion,the ribonucleases appeared to be differently regulated:some increased,some decreased and the others unchanged.However,after 72 hours of diazotrophic growth,all ribonucleases went back to the normal expression levels.Remarkably,we found that intracellular RNase E was specifically processed by certain proteases upon nitrogen starvation,with its C-terminal being degraded.We further proved that it was a divalent metalloprotease that participated in the process.Anabaena RNase E and E.coli RNase E share similar sequence features,with the N-terminal being the catalytic domain and the C-terminal being an unstructured region interacting with other proteins.Thus,the protease-mediated degradation of Anabaena RNase E C-terminal could be a novo mechanism regulating the RNA metabolism during the adaption to nitrogen-stavation.