Mutations of the act promoter in Myxococcus xanthus.
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.
Gronewold
Thomas M A
TM
Department of Biochemistry, Stanford University School of Medicine, Stanford, CA 94305-5329, USA.
Kaiser
Dale
D
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000502:physiology; D008969:Molecular Sequence Data; D009154:Mutation; D016941:Myxococcus xanthus / Q000235:genetics* / Q000502:physiology; D009876:Operon; D011401:Promoter Regions, Genetic; D012045:Regulatory Sequences, Nucleic Acid; D015398:Signal Transduction; D014157:Transcription Factors / Q000502:physiology
D001426:Bacterial Proteins; C104848:FruA protein, Myxococcus xanthus; D014157:Transcription Factors; C088618:lipase activator protein, Bacteria