FRUA, A PUTATIVE TRANSCRIPTION FACTOR ESSENTIAL FOR THE DEVELOPMENT OF MYXOCOCCUS-XANTHUS

A new developmental gene, fruA, of Myxococcus xanthus was cloned using a one-step cloning vector, Tn V. DNA sequencing of the wild-type alle le of the fruA gene indicated that the fruA gene encodes a protein of 229 amino acid residues with a calculated molecular weight of 24 672, The deduced amino acid sequence of FruA protein showed similarity to t hose of many bacterial regulatory proteins carrying a DNA-binding heli x-turn-helix motif. The transcription-initiation site of the froA gene was determined by a primer-extension experiment. Development of M. xa nthus cells with a disrupted fruA gene stopped at the stage of mound f ormation, Although cells were able to aggregate to form mounds, myxosp ores were not formed, By Northern and Western blot analysis, it was fo und that the fruA expression was not detected during vegetative growth but initiated at around 6h and reached the highest level at 12 h afte r the onset of development. Expression of the fruA gene was dependent on the expression of asg, bsg, csg, dsg, and esg genes, indicating tha t a series of intercellular signalling is necessary for the expression of the fruA gene, The effects of the fruA mutation on beta-galactosid ase expression of various developmentally regulated genes fused with t he lacZ gene were analysed; three developmental lacZ fusions (Omega n4 469, Omega 4273 and Omega 4500) were either poorly induced or not indu ced at all, while three other lacZ fusions (Omega 4408, Omega 4521 and Omega 4455) expressed at the early stage of development were normally induced but were unable to be repressed at a later stage of developme nt as in the wild-type strain, Interestingly, in the fruA mutant, fps (the gene for protein S) was not activated. From these results togethe r with analysis of the amino acid sequence of FruA, we propose that Fr uA is a putative transcription factor required for the development of M. xanthus.