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Journal of Bacteriology, February 2002, p. 1172-1179, Vol. 184, No. 4
0021-9193/01/$04.00+0     DOI: 10.1128/jb.184.4.1172-1179.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

act Operon Control of Developmental Gene Expression in Myxococcus xanthus

Thomas M. A. Gronewold{dagger}, and Dale Kaiser*

Departments of Biochemistry and of Developmental Biology, Stanford University School of Medicine, Stanford, California 94305-5329

Received 30 July 2001/ Accepted 15 November 2001

Cell-bound C-signal guides the building of a fruiting body and triggers the differentiation of myxospores. Earlier work has shown that transcription of the csgA gene, which encodes the C-signal, is directed by four genes of the act operon. To see how expression of the genes encoding components of the aggregation and sporulation processes depends on C-signaling, mutants with loss-of-function mutations in each of the act genes were investigated. These mutations were found to have no effect on genes that are normally expressed up to 3 h into development and are C-signal independent. Neither the time of first expression nor the rate of expression increase was changed in actA, actB, actC, or actD mutant strains. Also, there was no effect on A-signal production, which normally starts before 3 h. By contrast, the null act mutants have striking defects in C-signal production. These mutations changed the expression of four gene reporters that are related to aggregation and sporulation and are expressed at 6 h or later in development. The actA and actB null mutations substantially decreased the expression of all these reporters. The other act null mutations caused either premature expression to wild-type levels (actC) or delayed expression (actD), which ultimately rose to wild-type levels. The pattern of effects on these reporters shows how the C-signal differentially regulates the steps that together build a fruiting body and differentiate spores within it.

* Corresponding author. Mailing address: Departments of Biochemistry and of Developmental Biology, Stanford University School of Medicine, 279 Campus Dr., Stanford, CA 94305-5329. Phone: (650) 723-6165. Fax: (650) 725-7739. E-mail: luttman{at}cmgm.stanford.edu.

{dagger} Present address: Center of Advanced Studies and Research, 38111 Bonn, Germany.

Journal of Bacteriology, February 2002, p. 1172-1179, Vol. 184, No. 4
0021-9193/01/$04.00+0     DOI: 10.1128/jb.184.4.1172-1179.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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