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Journal of Bacteriology, January 2007, p. 369-376, Vol. 189, No. 2
0021-9193/07/$08.00+0     doi:10.1128/JB.01373-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Coordinate Expression of the Acetyl Coenzyme A Carboxylase Genes, accB and accC, Is Necessary for Normal Regulation of Biotin Synthesis in Escherichia coli{triangledown}

Ahmed M. Abdel-Hamid1 and John E. Cronan1,2*

Departments of Microbiology,1 Biochemistry, University of Illinois, Urbana, Illinois 618012

Received 29 August 2006/ Accepted 12 October 2006

Transcription of the biotin (bio) biosynthetic operon of Escherichia coli is negatively regulated by the BirA protein, an atypical repressor protein in that it is also an enzyme. The BirA-catalyzed reaction involves the covalent attachment of biotin to AccB, a subunit of acetyl coenzyme (acetyl-CoA) carboxylase. The two functions of BirA allow regulation of the bio operon to respond to the intracellular concentrations of both biotin and unbiotinylated AccB. We report here that bio operon expression is down-regulated by overproduction of AccC, another acetyl-CoA carboxylase subunit known to form a complex with AccB. This down-regulation is eliminated when AccB and AccC are coordinately overexpressed, but only when the AccB partner is competent to bind AccC. Under AccC overexpression conditions AccB is underbiotinylated. These findings can be explained by a model in which excess AccC sequesters AccB in a complex that is a poor substrate for biotinylation. The observed disruption of biotin synthesis and attachment provides an excellent rationale for the observation that in the vast majority of sequenced bacterial genomes AccB and AccC are encoded in a two-gene operon.

* Corresponding author. Mailing address: Department of Microbiology, University of Illinois, Urbana, IL 61801. Phone: (217) 333-7919. Fax: (217) 244-6697. E-mail: j-cronan{at}life.uiuc.edu.

{triangledown} Published ahead of print on 20 October 2006.

Journal of Bacteriology, January 2007, p. 369-376, Vol. 189, No. 2
0021-9193/07/$08.00+0     doi:10.1128/JB.01373-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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