A new regulatory circuit in ribosomal protein operons: S2-mediated control of the rpsB-tsf expression in vivo
Abstract
Autogenous regulation is a general strategy of balancing ribosomal protein synthesis in bacteria. Control mechanisms have been studied in detail for most of ribosomal protein operons, except for rpsB-tsf encoding essential r-protein S2 and elongation factor Ts, where even the promoter has remained unknown. By using single-copy translational fusions with the chromosomal lacZ gene and Western-blot analysis, we demonstrate here that S2 serves as a negative regulator of both rpsB and tsf expression in vivo, acting at a single target within the rpsB 5′-untranslated region (5′-UTR). As determined by primer extension, transcription of the Escherichia coli rpsB-tsf operon starts 162 nucleotides upstream of the rpsB initiation codon at a single promoter TGTGGTATAAA belonging to the extended −10 promoter class. Both the promoter signature and the 5′-UTR structure of the rpsB gene appear to be highly conserved in γ-proteobacteria. Deletion analysis of the rpsB 5′-UTR within rpsB′-′lacZ fusions has revealed that an operator region involved in the S2 autoregulation comprises conserved structural elements located upstream of the rpsB ribosome binding site. The S2-mediated autogenous control is impaired in rpsB mutants and, more surprisingly, in the rpsA mutant producing decreased amounts of truncated r-protein S1 (rpsA∷IS10), indicating that S2 might act as a repressor in cooperation with S1.
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Footnotes
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Reprint requests to: Irina V. Boni, Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry RAS, Ul. Miklukho-Maklaya 16/10, 117997 Moscow, Russia; e-mail: irina{at}humgen.siobc.ras.ru; fax: 7-495-330-65-38.
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Article published online ahead of print. Article and publication date are at http://www.rnajournal.org/cgi/doi/10.1261/rna.1099108.
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- Received March 26, 2008.
- Accepted May 12, 2008.
- Copyright © 2008 RNA Society