The Small RNA IstR Inhibits Synthesis of an SOS-Induced Toxic Peptide

• Published in: Current biology Vol. 14; no. 24; pp. 2271 - 2276
• Main Authors: Vogel, Jörg, Argaman, Liron, Wagner, E.Gerhart H., Altuvia, Shoshy
• Format: Journal Article
• Language: English
• Published: England Elsevier Inc 29.12.2004
• Subjects: Amino Acid Sequence; Base Sequence; Blotting, Northern; Comparative Study; Escherichia coli - genetics; Gene Expression Regulation, Bacterial; Models, Genetic; Molecular Sequence Data; Peptides - genetics; Peptides - metabolism; Peptides - toxicity; Peptides/genetics/metabolism/toxicity; RNA, Bacterial - genetics; RNA, Messenger - genetics; RNA, Messenger - metabolism; SOS Response (Genetics) - genetics; SOS Response (Genetics) - physiology; SOS Response (Genetics)/genetics/physiology; Bacterial; Research Support; Messenger/genetics/metabolism; RNA; Gene Expression Regulation; Genetic; U.S. Gov't; Blotting; Bacterial/genetics; Northern; Models; Non-U.S. Gov't; Non-P.H.S
• ISSN: 0960-9822; 1879-0445; 1879-0445
• DOI: 10.1016/j.cub.2004.12.003

More than 60 small RNAs (sRNA) have been identified in E. coli[1–7]. The functions of the majority of these sRNAs are still unclear. For the few sRNAs characterized, expression and functional studies indicate that they act under stress conditions [8–14]. Here, we describe a novel E. coli chromosome locus that is part of the SOS response to DNA damage. This locus encodes two sRNAs, IstR-1 and IstR-2, and a toxic peptide, TisB, encoded by tisAB mRNA. Transcription of tisAB and istR-2 is SOS regulated, whereas IstR-1 is present throughout growth. IstR-1 inhibits toxicity by base-pairing to a short region in the tisAB mRNA. This antisense interaction entails RNase III-dependent cleavage, thereby inactivating the mRNA for translation. In the absence of the SOS response, IstR-1 is present in high excess over its target. However, SOS induction leads to depletion of the IstR-1 pool, concomitant with accumulation of tisAB mRNA. Under such conditions, TisB exerts its toxic effect, slowing down growth. We propose that the inhibitory sRNA prevents inadvertent TisB synthesis during normal growth and, possibly, also limits SOS-induced toxicity. Our study adds the SOS regulon to the growing list of global regulatory circuits controlled by sRNA genes.