RNase J， a prokaryotic 5'-3' exo/endoribonuclease， contributes to mRNA decay， rRNA maturation and post-transcriptional regulation. Yet the processive-exoribonucleolysis mechanism remains obscure. Here， we solved the first RNA-free and RNA-bound structures of an archaeal RNase J， and through intensive biochemical studies provided detailed mechanistic insights into the catalysis and processivity. Distinct dimerization/tetramerization patterns were observed for archaeal and bacterial RNase Js， and unique archaeal Loops I and II were found involved in RNA interaction. A hydrogen-bond-network was identified for the first time that assists catalysis by facilitating efficient proton transfer in the catalyt... More
RNase J， a prokaryotic 5'-3' exo/endoribonuclease， contributes to mRNA decay， rRNA maturation and post-transcriptional regulation. Yet the processive-exoribonucleolysis mechanism remains obscure. Here， we solved the first RNA-free and RNA-bound structures of an archaeal RNase J， and through intensive biochemical studies provided detailed mechanistic insights into the catalysis and processivity. Distinct dimerization/tetramerization patterns were observed for archaeal and bacterial RNase Js， and unique archaeal Loops I and II were found involved in RNA interaction. A hydrogen-bond-network was identified for the first time that assists catalysis by facilitating efficient proton transfer in the catalytic center. A conserved 5'-monophosphate-binding pocket that coordinates the RNA 5'-end ensures the 5'-monophosphate preferential exoribonucleolysis. To achieve exoribonucleolytic processivity， the 5'-monophosphate-binding pocket and nucleotide +4 binding site anchor RNA within the catalytic track; the 5'-capping residue Leu37 of the sandwich pocket coupled with the 5'-monophosphate-binding pocket are dedicated to translocating and controlling the RNA orientation for each exoribonucleolytic cycle. The processive-exoribonucleolysis mechanism was verified as conserved in bacterial RNase J and also exposes striking parallels with the non-homologous eukaryotic 5'-3' exoribonuclease， Xrn1. The findings in this work shed light on not only the molecular mechanism of the RNase J family， but also the evolutionary convergence of divergent exoribonucleases.
