Unusual, Dual Endo- and Exonuclease Activity in the Degradosome Explained by Crystal Structure Analysis of RNase J1

RNase J is an essential enzyme in Bacillus subtilis with unusual dual endonuclease and 5'-to-3' exonuclease activities that play an important role in the maturation and degradation of mRNA. RNase J is also a component of the recently identified degradosome of B. subtilis. We report the crystal structure of RNase J1 from B. subtilis to 3.0 angstrom resolution, analysis of which reveals it to be in an open conformation suitable for binding substrate RNA. RNase J is a member of the beta-CASP family of zinc-dependent metallo-beta-lactamases. We have exploited this similarity in constructing a model for an RNase J1 :RNA complex. Analysis of this model reveals candidate-stacking interactions with conserved aromatic side chains, providing a molecular basis for the observed enzyme activity. Comparisons of the B. subtilis RNase J structure with related enzymes reveal key differences that provide insights into conformational changes during catalysis and the role of the C-terminal domain.