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Journal of Bacteriology, March 2007, p. 1836-1844, Vol. 189, No. 5
0021-9193/07/$08.00+0     doi:10.1128/JB.01618-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Mutations of the Act Promoter in Myxococcus xanthus{triangledown} ,{dagger}

Thomas M. A. Gronewold{ddagger} and Dale Kaiser*

Departments of Biochemistry and of Developmental Biology, Stanford University School of Medicine, Stanford, California 94305

Received 17 October 2006/ Accepted 12 December 2006

Mutations within the –12 and –24 elements provide evidence that the act promoter is recognized by sigma-54 RNA polymerase. Deletion of the –20 base pair, which lies between the two conserved elements of sigma-54 promoters, decreased expression by 90%. In addition, mutation of a potential enhancer sequence, around –120, led to an 80% reduction in act gene expression. actB, the second gene in the act operon, encodes a sigma-54 activator protein that is proposed to be an enhancer-binding protein for the act operon. All act genes, actA to actE, are expressed together and constitute an operon, because an in-frame deletion of actB decreased expression of actA and actE to the same extent. After an initially slow phase of act operon expression, which depends on FruA, there is a rapid phase. The rapid phase is shown to be due to the activation of the operon expression by ActB, which completes a positive feedback loop. That loop appears to be nested within a larger positive loop in which ActB is activated by the C signal via ActA, and the act operon activates transcription of the csgA gene. We propose that, as cells engage in more C signaling, positive feedback raises the number of C-signal molecules per cell and drives the process of fruiting body development forward.

* Corresponding author. Mailing address: Department of Developmental Biology, Beckman Center, B300, Stanford University School of Medicine, 279 Campus Drive, Stanford, CA 94305-5329. Phone: (650) 723-6165. Fax: (650) 725-7739. E-mail: kaiser{at}cmgm.stanford.edu.

{triangledown} Published ahead of print on 22 December 2006.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

{ddagger} Present address: Center of Advanced European Studies and Research, Ludwig-Erhard-Allee 2, 53175 Bonn, Germany.

Journal of Bacteriology, March 2007, p. 1836-1844, Vol. 189, No. 5
0021-9193/07/$08.00+0     doi:10.1128/JB.01618-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Ossa, F., Diodati, M. E., Caberoy, N. B., Giglio, K. M., Edmonds, M., Singer, M., Garza, A. G. (2007). The Myxococcus xanthus Nla4 Protein Is Important for Expression of Stringent Response-Associated Genes, ppGpp Accumulation, and Fruiting Body Development. J. Bacteriol. 189: 8474-8483 [Abstract] [Full Text]  


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