In vitro transcription of Myxococcus xanthus genes with RNA polymerase containing sigma(A), the major sigma factor in growing cells

Myxococcus xanthus is a Gram-negative bacterium that undergoes multicellular development upon starvation. We have developed a simple and rapid procedure for partial purification of RNA polymerase from growing M. xanthus cells, using heparin-agarose and DNA-cellulose chromatographies. In addition to core subunits, the enzyme contains one fairly abundant polypeptide of approximately 105 kDa. We have shown by Western blot analysis and protein sequencing that the 105-kDa polypeptide is sigma(A), the product of the M. xanthus sigA gene, Partially purified sigma(A) RNA polymerase, or holoenzyme reconstituted from sigma(A) and core RNA polymerase, transcribed in vitro the vegA and aphII genes that are known to be expressed in growing M. xanthus cells. Reconstituted sigma(A) RNA polymerase produced vegA mRNA in vitro with the same 5' end as vegA mRNA produced in vivo, demonstrating that initiation of transcription was accurate in vitro. These results provide biochemical evidence that sigma(A) is the major vegetative sigma factor of M. xanthus. To our knowledge, this is the first report of in vitro transcription of M. xanthus chromosomal genes, providing a foundation for further biochemical analysis of transcriptional regulatory mechanisms in a microbe that relies extensively on cell-cell interactions.