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Journal of Bacteriology, July 2006, p. 5167-5176, Vol. 188, No. 14
0021-9193/06/$08.00+0 doi:10.1128/JB.00318-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
4400 Promoter by the Essential Developmental Protein FruA
Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824
Received 3 March 2006/ Accepted 5 May 2006
The bacterium Myxococcus xanthus employs extracellular signals to coordinate aggregation and sporulation during multicellular development. Extracellular, contact-dependent signaling that involves the CsgA protein (called C-signaling) activates FruA, a putative response regulator that governs a branched signaling pathway inside cells. One branch regulates cell movement, leading to aggregation. The other branch regulates gene expression, leading to sporulation. C-signaling is required for full expression of most genes induced after 6 h into development, including the gene identified by Tn5 lac insertion
4400. To determine if FruA is a direct regulator of
4400 transcription, a combination of in vivo and in vitro experiments was performed.
4400 expression was abolished in a fruA mutant. The DNA-binding domain of FruA bound specifically to DNA upstream of the promoter 35 region in vitro. Mutations between bp 86 and 77 greatly reduced binding. One of these mutations had been shown previously to reduce
4400 expression in vivo and make it independent of C-signaling. For the first time, chromatin immunoprecipitation (ChIP) experiments were performed on M. xanthus. The ChIP experiments demonstrated that FruA is associated with the
4400 promoter region late in development, even in the absence of C-signaling. Based on these results, we propose that FruA directly activates
4400 transcription to a moderate level prior to C-signaling and, in response to C-signaling, binds near bp 80 and activates transcription to a higher level. Also, the highly localized effects of mutations between bp 86 and 77 on DNA binding in vitro, together with recently published footprints, allow us to predict a consensus binding site of GTCG/CGA/G for the FruA DNA-binding domain.
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