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Characterization of MazF_Sa, an Endoribonuclease from Staphylococcus aureus

Department of Microbiology and Immunology, Dartmouth Medical School, Hanover, New Hampshire 03755

Received 7 August 2007/ Accepted 2 October 2007

The mazEF homologs of Staphylococcus aureus, designated mazEF_sa, have been shown to cotranscribe with the sigB operon under stress conditions. In this study, we showed that MazEF_Sa, as with their Escherichia coli counterparts, compose a toxin-antitoxin module wherein MazF_Sa leads to rapid cell growth arrest and loss in viable CFU upon overexpression. MazF_Sa is a novel sequence-specific endoribonuclease which cleaves mRNA to inhibit protein synthesis. Using ctpA mRNA as the model substrate both in vitro and in vivo, we demonstrated that MazF_Sa cleaves single-strand RNA preferentially at the 5' side of the first U or 3' side of the second U residue within the consensus sequences VUUV' (where V and V' are A, C, or G and may or may not be identical). Binding studies confirmed that the antitoxin MazE_Sa binds MazF_Sa to form a complex to inhibit the endoribonuclease activity of MazF_Sa. Contrary to the system in E. coli, exposure to selected antibiotics augmented mazEF_sa transcription, akin to what one would anticipate from the environmental stress response of the sigB system. These data indicate that the mazEF system of S. aureus differs from the gram-negative counterparts with respect to mRNA cleavage specificity and antibiotic stresses.

Published ahead of print on 12 October 2007.

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