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Journal of Bacteriology, December 1998, p. 6154-6163, Vol. 180, No. 23
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Catabolite Regulation of the Bacillus subtilis ctaBCDEF Gene Cluster

Xuemin Liu1 and Harry W. Taber1,2,3,*

Department of Microbiology, Immunology, and Molecular Genetics, Albany Medical College,1 Wadsworth Center, New York State Department of Health,2 and School of Public Health, State University of New York at Albany,3 Albany, New York 12201

Received 26 March 1998/Accepted 16 September 1998

Bacillus subtilis cytochrome c oxidase caa3 is encoded by the ctaCDEF genes at the ctaABCDEF locus, with the ctaBCDEF genes organized as an operon-like unit. A dyad symmetry sequence and a catabolite response element homolog can be recognized in the 240-bp intercistronic region between ctaB and ctaC. ctaB'-lacZ and ctaBCD'-lacZ transcriptional fusions integrated at the native locus were used to study catabolite effects on transcription of the ctaB and ctaCDEF genes. In Schaeffer's medium lacking glucose, ctaBCD'-lacZ was expressed at a very low level during the exponential phase, and expression increased about 30-fold 2 h after entry into the stationary phase. In the presence of 0.5% glucose, ctaBCD'-lacZ expression was totally repressed. In contrast to ctaBCD'-lacZ, ctaB'-lacZ was constitutively expressed regardless of carbon source. The ctaCDEF genes were separated from ctaB by insertion of plasmids carrying selectable markers in such a way that the ctaCDEF and ctaB transcription units remained intact. Enzymatic assays of caa3 with these constructs, showed that ctaCDEF was not expressed independently of ctaB. Also, when a 'ctaB-ctaC'-lacZ fusion (containing the ctaB-ctaC intercistronic region) was placed at a remote nonessential locus, beta -galactosidase activity could not be detected. The absence of a promoter in the ctaB-ctaC intercistronic space also was indicated by the inability to detect ctaC-specific transcripts with RNase protection assays, primer extension, and rapid amplification of 5' cDNA ends. Direct mRNA measurements showed that, in the presence of 0.5% glucose, ctaBCDEF transcripts terminated at the 3' end of the putative stem-loop structure and the distal portion was down-regulated. A possible mechanism for ctaCDEF gene regulation is suggested. Catabolite repression of ctaBCD'-lacZ was partly dependent on CcpA but was independent of HPr. The expression of ctaBCDEF also appears to require the strC, ctaA, and resD-resE gene products.

* Corresponding author. Mailing address: Wadsworth Center, New York State Department of Health, P.O. Box 22002, Albany, NY 12201-2002. Phone: (518) 473-2760. Fax: (518) 473-2639. E-mail: harry.taber{at}wadsworth.org.

Journal of Bacteriology, December 1998, p. 6154-6163, Vol. 180, No. 23
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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