MYXOCOCCUS-XANTHUS SASS ENCODES A SENSOR HISTIDINE KINASE REQUIRED FOR EARLY DEVELOPMENTAL GENE-EXPRESSION

Initiation of Myxococcus xanthus multicellular development requires in tegration of information concerning the cells' nutrient status and den sity. A gain-of function mutation, sasB7, that bypasses both the starv ation and high cell density requirements for developmental expression of the 4521 reporter gene, maps to the sasS gene. The wild-type sasS g ene was cloned and sequenced. This gene is predicted to encode a senso r histidine protein kinase that appears to be a key element in the tra nsduction of starvation and cell density inputs. The sasS null mutants express 4521 at a basal level, form defective fruiting bodies, and ex hibit reduced sporulation efficiencies. These data indicate that the w ild-type sasS gene product functions as a positive regulator of 4521 e xpression and participates in M. xanthus development. The N terminus o f SasS is predicted to contain two transmembrane domains that would lo cate the protein to the cytoplasmic membrane. The sasB7 mutation, an E 139K missense mutation, maps to the predicted N-terminal periplasmic r egion. The C terminus of SasS contains all of the conserved residues t ypical of the sensor histidine protein kinases. SasS is predicted to b e the sensor protein in a two-component system that integrates informa tion required for M. xanthus developmental gene expression.