DEVRS, AN AUTOREGULATED AND ESSENTIAL GENETIC-LOCUS FOR FRUITING BODYDEVELOPMENT IN MYXOCOCCUS-XANTHUS

Two Tn5 lac insertions into the Myxococcus genome at sites OMEGA4414 a nd OMEGA4473, which are separated by 550 nucleotides, inactivate fruit ing body development. Sporulation is decreased 100- to 10,000-fold. At least two genes, devR and devS, are transcribed in this region, proba bly as an operon. Expression of devR begins by 6 h after starvation ha s initiated development. On the basis of their nucleotide sequences, d evR and devS are expected to encode proteins of 302 and 214 amino acid s, respectively. Dev+ function can be restored by a segment of 7.8 kb cloned from the devRS region of wild-type cells. Two experiments show that devR expression is under strong negative autoregulation. Beta-Gal actosidase is expressed at a higher level from a transcriptional devR: :lacZ fusion when the fused operon is in a dev strain than when it is in the dev/dev+ genetic background of a partial diploid. There is more mRNA accumulation from the devRS region in the dev strain than in a r escued dev/dev+ tandem duplication strain. Sporulation rescue is corre lated with some degree of negative autoregulation, even though sporula tion is not inversely proportional to beta-galactosidase expression fr om OMEGA4414. A second level of regulation is suggested by complementa tion of dev by dev+ in duplication strains. The expression of devRS, m easured by sporulation levels, differs 1,000-fold when devRS+ is moved from a distance of 20 kb to 3 Mb from the mutant devRS locus. Express ion of devR is also dependent on the cell density at which development is initiated, a third level of regulation. Multiple levels of regulat ion suggest that devRS is a switch required to activate completion of aggregation and sporulation.