title: Translational control of small heat shock genes in mesophilic and thermophilic cyanobacteria by RNA thermometers.
abstract: Cyanobacteria constitute a heterogeneous phylum of oxygen-producing, photosynthetic prokaryotes. They are susceptible to various stress conditions like heat, salt, or light stress, all inducing the cyanobacterial heat shock response (HSR). Cyanobacterial small heat shock proteins (sHsps) are known to preserve thylakoid membrane integrity under stress conditions, thereby protecting the photosynthesis machinery. In Synechocystis sp PCC 6803, synthesis of the sHsp Hsp17 is regulated by an RNA thermometer (RNAT) in the 5'-untranslated region (5'-UTR) of the hsp17 mRNA. RNATs are direct temperature sensors that control expression of many bacterial heat shock and virulence genes. They hinder translation at low temperatures by base pairing, thus blocking ribosome access to the mRNA.   To explore the temperature range in which RNATs act, we studied various RNAT candidates upstream of sHsp genes from mesophilic and thermophilic cyanobacteria. The mesophilic cyanobacteria Anabaena variabilis and Nostoc sp chromosomally encode two sHsps each. Reporter gene studies suggested RNAT-mediated post-transcriptional regulation of shsp expression in both organisms. Detailed structural analysis of the two A. variabilis candidates revealed two novel RNAT types. The first, avashort, regulates translation primarily by masking of the AUG translational start codon. The second, featuring an extended initial hairpin, thus named avalong, presumably makes use of complex tertiary interaction. The 5'-UTR of the small heat shock gene hspA in the thermophile Thermosynechococcus elongatus is predicted to adopt an extended secondary structure. Structure probing revealed that the ribosome binding site was blocked at temperatures below 55 °C. The results of this study demonstrate that cyanobacteria commonly use RNATs to control expression of their small heat shock genes.
authors.affiliation: Microbial Biology; Ruhr University Bochum; Bochum, Germany.
authors.forename: Annika
authors.initials: A
authors.lastname: Cimdins
authors.affiliation: Microbial Biology; Ruhr University Bochum; Bochum, Germany.
authors.forename: Birgit
authors.initials: B
authors.lastname: Klinkert
authors.affiliation: Microbial Biology; Ruhr University Bochum; Bochum, Germany.
authors.forename: Ursula
authors.initials: U
authors.lastname: Aschke-Sonnenborn
authors.affiliation: Microbial Biology; Ruhr University Bochum; Bochum, Germany.
authors.forename: Friederike M
authors.initials: FM
authors.lastname: Kaiser
authors.affiliation: Microbial Biology; Ruhr University Bochum; Bochum, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Kortmann
authors.affiliation: Microbial Biology; Ruhr University Bochum; Bochum, Germany.
authors.forename: Franz
authors.initials: F
authors.lastname: Narberhaus
mesh_terms: D001483:Base Sequence; D018387:Codon, Initiator; D000458:Cyanobacteria / Q000235:genetics* / Q000378:metabolism; D015870:Gene Expression; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D050888:Heat-Shock Proteins, Small / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D018869:Heat-Shock Response / Q000235:genetics; D006358:Hot Temperature; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D014176:Protein Biosynthesis; D012329:RNA, Bacterial / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D013696:Temperature; D020506:Untranslated Regions
chemical_list: D018387:Codon, Initiator; D050888:Heat-Shock Proteins, Small; D012329:RNA, Bacterial; D020506:Untranslated Regions
keywords: RNA thermometer; cyanobacteria; heat shock response; post-transcriptional control; small heat shock protein
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