The Interaction Between RNase E And PNPase In Anabaena SP.PCC 7120

RNA degradosome,an RNase E-based RNA-degrading complex,plays an importantrole in RNA processing,maturation and degradation,has been found in several bacteria.The RNA degradosomes from different species share some key components but are not identical.In Escherichia coli,the RNA degradosome has the core components RNase E,PNPase,Rh1B and Enolase;while in Caulobacter crescentus,the components are RNase E,PNPase,Rh1B and Aconitase.RNase E is also present in cyanobacteria and many other bacterial species;however,it is yet unknown whether RNase E-based RNA degradating complex commonly exists in these organisms.Alignment analysis of all known cyanobacterial RNase E proteins revealed that their N-terminal regions(catalytic)are highly conserved and show great similarity(more than 50%)to the counterpart region in E.coli RNase E,while their C-terminal regions(non-catalytic)are quite different from that of E.coli.Within the C-terminals of cyanobacterial RNase E,we have identified 4 concerved and 3 variable subregions(named as C1,C2,C3,C4,V1,V2 and V3,respectively).Among them,C2 and C4 are rich of arginine residues.In E.coli,the C-terminal of RNase E serves as the scaffold recuiting the RNA degrdosome components of PNPase,Rh1B and Enolase.Does cyanobacterial RNase E behave similarly in vivo?Here,we explored the question in the filamentous and diazotropHic cyanobacterium Anabaena PCC 7120.We investigated the interaction between the C-terminal of Anabaena RNase E(AnaRneC)and several other proteins that are homolous to some RNA degradosome components indentified in other organisms.By dot-blot assay,PNPase was found to interact with AnaRneC in vitro.PNPase could be isolated together with the histagged AnaRneC when the later was expressed in Anabaena cells,indicating their interaction in vivo.Further investigation showed that the deletion of the C4 region(RRRRRRSSA)in AnaRneC resulted in the failure of PNPase binding,whereas the GFP protein fused with C4 obtained the capacity to bind to PNPase.The data above indicate that C4 is the right site via which Anabaena RNase E interacts with PNPase.We also found that the RNase E and PNPases from another unicellular cyanobacterium,Synechocystis PCC 6803,could form a complex in the same way,implying that the interaction of RNase E-PNPase commonly present in cyanobacteria.