SIGMA(54), A VITAL PROTEIN FOR MYXOCOCCUS-XANTHUS

The rpoN gene encoding the transcription factor sigma(54) in Myxococcu s xanthus has been cloned using a heterologous rpoN probe. The sequenc e of the cross-hybridizing DNA confirmed the existence of an ORF 1518 bp long that encodes a well conserved member of the sigma(54) family o f sigma factors. Low- as well as high stringency hybridizations detect ed only a single rpoN gene in the M. xanthus chromosome. In other bact eria, sigma(54) is an alternative sigma, and null mutants are viable. However, all attempts to construct a strain containing a null mutation in the M. xanthus rpoN have been unsuccessful. Partial diploids of rp oN(+)/rpoN null are viable. Recombination experiments with such partia l diploids showed the impossibility of constructing, either by segrega tion or by transduction, a viable null haploid under any of a wide ran ge of growth conditions. The product of the rpoN gene, sigma(54), ther efore appears to be essential for growth in M. xanthus.