Characterization of regulatory mechanisms of cell-cell interaction-dependent genes of Myxococcus xanthus

Myxococcus xanthus is a gram-negative, rod-shaped soil bacterium that undergoes multicellular development in response to nutrient limitation. Upon starvation, many thousands of cells move in a coordinated fashion into aggregation centers and construct multicellular structures known as fruiting bodies, in which individual cells undergo morphological and physiological changes to form dormant ovoid-shaped spores. The progression through fruiting body formation and sporulation is highly coordinated and involves at least five extracellular signaling interactions. These five signaling interactions are also needed for the proper expression of developmental genes.; One of the extracellular signals is C-signaling, which is required for aggregation and sporulation. C-signaling mutants initiate development normally but fail to form compact fruiting bodies and spores. Of the genes that have been examined, almost every one expressed at six hours or later in development exhibits reduced or abolished expression in C-signaling mutant cells.; To understand how extracellular C-signaling regulates gene expression during development, the regulatory regions of several C-signal-dependent genes have been characterized. Like these genes, the operon identified by Tn5 lac Ω4514 is expressed at about the same time during development, but its expression does not depend on C-signaling. The developmental regulation of this operon has been investigated. Based on sequence similarity, the Ω4514 operon may encode an enzyme involved in glutamate fermentation and a transcriptional regulator. The promoter of the operon shares similarity with promoters that are expressed during growth and the Ω4514 promoter can be transcribed in vitro by the major vegetative RNA polymerase. Developmental regulation of Ω4514 expression is complex, involving negative regulation by the product of the first gene in the operon and positive regulation by one or more transcriptional activators.; Developmental expression of the Ω4403 gene is absolutely dependent on C-signaling and on DNA sequences extending to −80 relative to the start site of transcription. A search for regulatory proteins that interact with the upstream region has been carried out. No protein likely to mediate C-signal-dependent expression of Ω4403 was identified.