title: Positive regulation of psbA gene expression by cis-encoded antisense RNAs in Synechocystis sp. PCC 6803.
abstract: The D1 protein of photosystem II in the thylakoid membrane of photosynthetic organisms is encoded by psbA genes, which in cyanobacteria occur in the form of a small gene family. Light-dependent up-regulation of psbA gene expression is crucial to ensure the proper replacement of the D1 protein. To gain a high level of gene expression, psbA transcription can be enhanced by several orders of magnitude. Recent transcriptome analyses demonstrated a high number of cis-encoded antisense RNAs (asRNAs) in bacteria, but very little is known about their possible functions. Here, we show the presence of two cis-encoded asRNAs (PsbA2R and PsbA3R) of psbA2 and psbA3 from Synechocystis sp. PCC 6803. These asRNAs are located in the 5' untranslated region of psbA2 and psbA3 genes. Their expression becomes up-regulated by light and down-regulated by darkness, similar to their target mRNAs. In the PsbA2R-suppressing strain [PsbA2R(-)], the amount of psbA2 mRNA was only about 50% compared with the control strain. Likewise, we identified a 15% lowered activity of photosystem II and a reduced amount of the D1 protein in PsbA2R(-) compared with the control strain. The function of PsbA2R in the stabilization of psbA2 mRNA was shown from in vitro RNase E assay when the AU box and the ribosome-binding site in the 5' untranslated region of psbA2 mRNA were both covered by PsbA2R. These results add another layer of complexity to the mechanisms that contribute to psbA gene expression and show PsbA2R as a positively acting factor to achieve a maximum level of D1 synthesis.
authors.affiliation: Department of Biochemistry and Food Chemistry, Molecular Plant Biology, University of Turku, FI-20014 Turku, Finland.
authors.forename: Isamu
authors.initials: I
authors.lastname: Sakurai
authors.forename: Damir
authors.initials: D
authors.lastname: Stazic
authors.forename: Marion
authors.initials: M
authors.lastname: Eisenhut
authors.forename: Eerika
authors.initials: E
authors.lastname: Vuorio
authors.forename: Claudia
authors.initials: C
authors.lastname: Steglich
authors.forename: Wolfgang R
authors.initials: WR
authors.lastname: Hess
authors.forename: Eva-Mari
authors.initials: EM
authors.lastname: Aro
mesh_terms: D020121:5' Untranslated Regions; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D003624:Darkness; D004722:Endoribonucleases / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D008027:Light; D008969:Molecular Sequence Data; D016296:Mutagenesis; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000378:metabolism*; D020871:RNA Stability; D016372:RNA, Antisense / Q000235:genetics*; D012329:RNA, Bacterial / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D038621:Regulatory Sequences, Ribonucleic Acid; D046939:Synechocystis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects; D020524:Thylakoids / Q000378:metabolism; D014158:Transcription, Genetic; D015854:Up-Regulation
chemical_list: D020121:5' Untranslated Regions; D001426:Bacterial Proteins; D045332:Photosystem II Protein Complex; D016372:RNA, Antisense; D012329:RNA, Bacterial; D012333:RNA, Messenger; D011994:Recombinant Proteins; D038621:Regulatory Sequences, Ribonucleic Acid; C422369:photosystem II, psbA subunit; D004722:Endoribonucleases; C022537:ribonuclease E