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Genetic Dissection of the Light-Inducible carQRS Promoter Region of Myxococcus xanthus

David E. Whitworth, Samantha J. Bryan, Andrew E. Berry, Simon J. McGowan, and David A. Hodgson^*

Department of Biological Sciences, University of Warwick, Coventry, United Kingdom

Received 24 June 2004/ Accepted 24 August 2004

In Myxococcus xanthus photoprotective carotenoids are produced in response to illumination due to regulated expression of carotenoid biosynthesis genes at two loci. Induction of the carotenogenesis regulon is dependent on expression of the carQRS operon. The first gene product of the operon, CarQ, is a sigma factor belonging to the ECF family and is responsible for light-dependent initiation of transcription at the carQRS promoter. We defined the minimal carQRS promoter as a 145-bp fragment of DNA upstream of the carQRS transcriptional start site, which includes the promoter for a divergent gene, gufA. In order to elucidate regions with the promoter required for activity, point mutations were introduced into the carQRS promoter between positions –151 and 6. While most sequence changes abolished carQRS promoter activity, two changes enhanced promoter activity and two changes caused the mutant promoter to become constitutive and independent of CarQ. The promoter-null point mutations and 6-bp deletion mutations implied that the carQRS promoter requires a functional gufA promoter for transcriptional activity and vice versa. By mapping the extent of the promoter region, identifying sequences important for promoter activity, and highlighting potential topological effects, we provide a foundation for further analysis of the carQRS promoter.

D.E.W. and S.J.B. contributed equally to this work.

Present address: Wellcome Trust Genome Campus, Hinxton, Cambridgeshire, CB10 1SA, United Kingdom.

Present address: The Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Headington, Oxford, OX3 9DS, United Kingdom.

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