The rpoN gene encoding the transcription factor σ~54 in Myxococcus xanthus has been cloned using a heterologous rpoN probe. The sequence of the cross- hybridizing DNA confirmed the existence of an ORF 1518 bp long that encodes a well conserved member of the σ~54 family of σ factors. Low- as well as high-stringency hybridizations detected only a single rpoN gene in the M. xanthus chromo- some. In other bacteria, σ~54 is an alternative σ, and null mutants are viable.
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