Transcript analysis of the Halothiobacillus neapolitanus cso operon
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ORIGINAL PAPER
Transcript analysis of the Halothiobacillus neapolitanus cso operon Fei Cai · Sabine Heinhorst · Jessup M. Shively · Gordon C. Cannon
Received: 17 May 2007 / Revised: 13 August 2007 / Accepted: 31 August 2007 / Published online: 27 September 2007 © Springer-Verlag 2007
Abstract Carboxysomes are polyhedral microcompartments that sequester the CO2-Wxing enzyme ribulose 1,5bisphosphate carboxylase/oxygenase in many autotrophic bacteria. Their protein constituents are encoded by a set of tightly clustered genes that are thought to form an operon (the cso operon). This study is the Wrst to systematically address transcriptional regulation of carboxysome protein expression. QuantiWcation of transcript levels derived from the cso operon of Halothiobacillus neapolitanus, the sulfur oxidizer that has emerged as the model organism for carboxysome structural and functional studies, indicated that all cso genes are transcribed, albeit at diVerent levels. Combined with comparative genomic evidence, this study supports the premise that the cso gene cluster constitutes an operon. Characterization of transcript 5⬘- and 3⬘-ends and examination of likely regulatory sequences and secondary structure elements within the operon suggested potential strategies by which the vastly diVerent levels of individual carboxysome proteins in the microcompartment could have arisen. Keywords Carboxysome operon · Halothiobacillus neapolitanus · Transcription · Real-time PCR
Communicated by Friedrich Widdel. F. Cai · S. Heinhorst · J. M. Shively · G. C. Cannon (&) Department of Chemistry and Biochemistry, The University of Southern Mississippi, 118 College Dr. #5043, Hattiesburg, MS 39406-0001, USA e-mail: [email protected] J. M. Shively Department of Genetics and Biochemistry, Clemson University, Clemson, SC 29634-1903, USA
Introduction Carboxysomes are polyhedral protein microcompartments found in all cyanobacteria and in many chemolithoautotrophs. These prokaryotic “organelles” enhance the catalytic ability of the rather ineYcient carbon dioxide Wxing enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO, encoded by cbbL and cbbS) sequestered within. The mechanism by which the microcompartment contributes to the catalytic eYciency of RubisCO is only partially understood but in the - (cso-) type carboxysomes involves a -carbonic anhydrase activity that is known to be tightly associated with the carboxysome shell (So et al. 2004; Heinhorst et al. 2006b; Sawaya et al. 2006). Recently, the structures of the major shell components, the CsoS1 and CcmK proteins of - and -carboxysomes, respectively, have been elucidated and have yielded novel insights into the architecture and function of the microcompartments’ protein shell (Kerfeld et al. 2005; Tsai et al. 2007). While the exact protein composition of cyanobacterial - (ccm-) carboxysomes is not known due to technical diYculties related to their puriWcation, the polypeptides of -carboxysomes have been very well characterized in the sulfur oxidizer Halothiobacillus ne
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