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Journal of Bacteriology, May 2000, p. 2438-2444, Vol. 182, No. 9
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

A sigma 54 Activator Protein Necessary for Spore Differentiation within the Fruiting Body of Myxococcus xanthus

Lisa Gorski,dagger Thomas Gronewold, and Dale Kaiser*

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

Received 6 December 1999/Accepted 9 February 2000

Insertion of an internal DNA fragment into the act1 gene, which encodes one of several sigma 54-activator proteins in Myxococcus xanthus, produced a mutant defective in fruiting body development. While fruiting-body aggregation appears normal in the mutant, it fails to sporulate (<10-6 the wild-type number of viable spores). The A and C intercellular signals, which are required for sporulation, are produced by the mutant. But, while it produces A-factor at levels as high as that of the wild type, the mutant produces much less C-signal than normal, as measured either by C-factor bioassay or by the total amount of C-factor protein detected with specific antibody. Expression of three C-factor-dependent reporters is altered in the mutant: the level of expression of Omega 4414 is about 15% of normal, and Omega 4459 and Omega 4403 have alterations in their time course. Finally, the methylation of FrzCD protein is below normal in the mutant. It is proposed that Act1 protein responds to C-signal reception by increasing the expression of the csgA gene. This C-signal-dependent increase constitutes a positive feedback in the wild type. The act1 mutant, unable to raise the level of csgA expression, carries out only those developmental steps for which a low level of C-signaling is adequate.

* Corresponding author. Mailing address: Department of Developmental Biology, Beckman Center, B300, Stanford University School of Medicine, Stanford, CA 94305-5329.

dagger Present address: Western Regional Research Center, USDA/ARS, Albany, CA 94710.

Journal of Bacteriology, May 2000, p. 2438-2444, Vol. 182, No. 9
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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