The Myxococcus xanthus socE and csgA genes are regulated by the stringent response

Disruption of the Myxococcus xanthus socE gene bypasses the requirement for the cell contact-dependent C-signalling system mediated by CsgA and restor es fruiting body morphogenesis and spore differentiation. The socE gene has been identified by genetic complementation, cloned and sequenced. SocE is highly basic, unique and is predicted to be a soluble protein with a molecu lar size of 53.6 kDa. The socE and csgA genes have opposite transcription p atterns during the M. xanthus life cycle. socE expression is high in growin g cells and declines during the early stages of development. Expression of csgA is low in vegetative cells and increases during development. socE tran scription is negatively regulated by the stringent response, the major amin o acid-sensing pathway in M. xanthus. A relA null mutation, which eliminate s the stringent response, prevents the decline in socE expression normally observed at the onset of development. CsgA is positively regulated by the s tringent response and is negatively regulated by socE. A relA mutation virt ually eliminates developmental csgA expression. Expression of socE in Esche richia coli leads to a rapid loss of viability in relA(-) cells during stat ionary phase, suggesting a relationship with the stringent response.