Abstract
The essential homotetrameric endoribonuclease RNase E of Escherichia coli participates in global RNA turnover as well as stable RNA maturation. The protomer's N-terminal half (residues 1-529) bears the catalytic, allosteric, and tetramerization domains, including the active site residues D303 and D346. The C-terminal half (CTH, residues 530-1061) is dispensable for viability. We have previously described a phenomenon of recessive resurrection in RNase E that requires the CTH, wherein the wild-type homotetramer apparently displays nearly identical activity in vivo as a heterotetramer comprising three catalytically dead subunits (with D303A or D346A substitutions) and one wild-type subunit. Here, we show that recessive resurrection is exhibited even in dimeric RNase E with the CTH, and that it is largely dependent on the presence of a membrane-targeting-sequence motif (residues 565-582). A single F575E substitution also impaired recessive resurrection, whereas other CTH motifs (such as those for binding of RNA or of partner proteins) were dispensable. The phenomenon was independent of RNA 5'-monophosphate sensing by the enzyme. We propose that membrane-anchoring of RNase E renders it processive for endoribonucleolytic action, and that recessive resurrection and dominant negativity associated with mutant protomers are mutually exclusive manifestations of, respectively, processive and distributive catalytic mechanisms in a homo-oligomeric enzyme.