title: SigmaB regulates ccrAB expression and SCCmec excision in methicillin-resistant Staphylococcus aureus.
abstract: Methicillin-resistant Staphylococcus aureus (MRSA) is a worldwide pathogen that is resistant to practically the entire class of β-lactam antibiotics due to the presence of the mecA gene. The mecA gene is located on a large mobile genetic element referred to as staphylococcal cassette chromosome mec (SCCmec), and the excision and integration of SCCmec are mediated by the Ccr recombinase encoded by ccrAB or ccrC, which are also located on SCCmec. Previous studies have shown that the ccrAB genes are only expressed in a minority of cells and that their expression levels can be affected by certain environmental stimuli, but the molecular mechanisms controlling these phenotypes remain elusive. Here, we found that overexpression of SigB can dramatically enhance ccrA transcription and SCCmec excision in MRSA strain N315, revealing an important role for this alternative sigma factor in the lateral transfer of SCCmec. Further primer extension-blot analysis and 5'RACE (Rapid Amplification of cDNA Ends) indicated that an unrecognized SigB-dependent promoter region, which exists in certain SCCmec type II and IV strains, is responsible for the enhancement, and the ccrAB genes are in fact transcribed in a two-promoter pattern with a low activity of the SigB-dependent promoter under normal growth conditions.
authors.affiliation: CAS Key Laboratory of Innate Immunity and Chronic Disease, School of Life Sciences and Medical Center, University of Science and Technology of China, Hefei, Anhui 230027, China.
authors.forename: Shijie
authors.initials: S
authors.lastname: Zhang
authors.affiliation: CAS Key Laboratory of Innate Immunity and Chronic Disease, School of Life Sciences and Medical Center, University of Science and Technology of China, Hefei, Anhui 230027, China.
authors.forename: Xueqin
authors.initials: X
authors.lastname: Shu
authors.affiliation: CAS Key Laboratory of Innate Immunity and Chronic Disease, School of Life Sciences and Medical Center, University of Science and Technology of China, Hefei, Anhui 230027, China; Hefei National Laboratory for Physical Sciences at Microscale, Hefei, Anhui 230027, China. Electronic address: sunb@ustc.edu.cn.
authors.forename: Baolin
authors.initials: B
authors.lastname: Sun
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D015870:Gene Expression; D015964:Gene Expression Regulation, Bacterial; D055624:Methicillin-Resistant Staphylococcus aureus / Q000235:genetics*; D011401:Promoter Regions, Genetic; D045522:Recombinases / Q000096:biosynthesis* / Q000235:genetics; D012808:Sigma Factor / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D045522:Recombinases; C079011:SigB protein, Bacteria; D012808:Sigma Factor
keywords: CcrAB expression; CcrAB gene organization; Methicillin-resistant Staphylococcus aureus; SCCmec excision; SigmaB