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Co-transcription of the celC gene cluster in Clostridium thermocellum
- Newcomb, Michael, Millen, Jonathan, Chen, Chun-Yu, Wu, J. H. David
- Applied microbiology and biotechnology 2011 v.90 no.2 pp. 625-634
- Clostridium thermocellum, Northern blotting, bacteria, cellulosome, endo-1,4-beta-glucanase, gene expression, glucose, multigene family, operon, transcription (genetics)
- Clostridium thermocellum, an anaerobic, thermophilic, and ethanogenic bacterium produces a large cellulase complex termed the cellulosome and many free glycosyl hydrolases. Most cellulase genes scatter around the genome. We mapped the transcripts of the six-gene cluster celC–glyR3–licA–orf4–manB–celT and determined their transcription initiation sites by primer extension. Northern blot showed that celC–glyR3–licA were co-transcribed into a polycistronic messenger with the transcription initiation site at −20 bp. Furthermore, RT-PCR mapping showed that manB and celT, two cellulosomal genes immediately downstream, were co-transcribed into a bicistronic messenger with the initiation site at −233 bp. In contrast, rf4 was transcribed alone with the two initiation sites at −130 and −138 bp, respectively. Finally, quantitative RT-PCR analysis showed that celC, glyR3, and licA were coordinately induced by growing on laminarin, a β-1,3 glucan. Gene expression peaked at the late exponential phase. Taking together with our previous report that GlyR3 binds to the celC promoter in the absence of laminaribiose, a β-1,3 glucose dimer, these results indicate that celC, glyR3, and licA form an operon repressible by GlyR3 and inducible by laminaribiose, signaling the availability of β-1,3 glucan. The celC operon is the first glycosyl hydrolase operon reported in this bacterium.