Myxococcus xanthus sasS encodes a sensor histidine kinase required for early developmental gene expression

Abstract

Initiation of Myxococcus xanthus multicellular development requires integration of information concerning the cells' nutrient status and density. A gain-of-function mutation, sasB7, that bypasses both the starvation and high cell density requirements for developmental expression of the 4521 reporter gene, maps to the sasS gene. The wild-type sasS gene was cloned and sequenced. This gene is predicted to encode a sensor histidine protein kinase that appears to be a key element in the transduction of starvation and cell density inputs. The sasS null mutants express 4521 at a basal level, form defective fruiting bodies, and exhibit reduced sporulation efficiencies. These data indicate that the wild-type sasS gene product functions as a positive regulator of 4521 expression and participates in M. xanthus development. The N terminus of SasS is predicted to contain two transmembrane domains that would locate the protein to the cytoplasmic membrane. The sasB7 mutation, an E139K missense mutation, maps to the predicted N-terminal periplasmic region. The C terminus of SasS contains all of the conserved residues typical of the sensor histidine protein kinases. SasS is predicted to be the sensor protein in a two-component system that integrates information required for M. xanthus developmental gene expression. Multicellular development of Myxococcus xanthus is initiatedby nutrient limitation and proceeds only if these gram-negative soil bacteria are at high density. More than 10 5 cells aggregate to form an organized mound, termed a fruiting body, inside of which the rod-shaped cells differentiate into environmentally resistant ovoid myxospores. This developmental program ensures the survival of the organism until nutrients are available and the spores can germinate (10, 11).M. xanthus cells sense their nutrient status and density by using two different signals. Nutrient limitation is sensed, at least in part, by a rise in intracellular guanosine penta-and tetraphosphate ([p]ppGpp) levels (55). Cell density is sensed through A signal, a specific subset of amino acids at an extracellular concentration greater than 10 M (36). The A signal is presumably generated when extracellular proteinases degrade the surface proteins of developing cells (35,49). If the cells are at a density greater than about 3 ϫ 10 8 /ml, apparently the concentration of extracellular amino acids and peptides exceeds the critical A-signal threshold concentration (36). The transduction of the starvation and A signals and integration of this information within the first 1 to 2 h of development allow the cells to determine if conditions are appropriate to proceed through the early stages of fruiting body development (15,26).The expression of one class of genes expressed during early development requires independent input from both starvation and A signals (4, 25). The best characterized member of this class is the gene 4521, whose expression is monitored by a Tn5 lac transcriptional fusion, ⍀4521 (31). In wild-type cells 1 to 2 h after starvation at high de...

Identification of the Ω4406 Regulatory Region, a Developmental Promoter of Myxococcus xanthus , and a DNA Segment Responsible for Chromosomal Position-Dependent Inhibition of Gene Expression

“…The results suggested that A-signaling is required in the first few hours of development for the expression of most developmental genes. The response to A-signaling involves the SasS-SasRSasN histidine kinase-response regulator-negative regulator three-component signal transduction system (59,60). By measuring expression of Tn5 lac fusions in a csgA mutant, it was revealed that C-signaling begins to be required at about 6 h into development (27).…”

Genetic Studies ofmrp, a Locus Essential for Cellular Aggregation and Sporulation ofMyxococcus xanthus

“…Through extensive genetic and biochemical studies, a number of regulatory proteins thought to be involved in cellular aggregation and sporulation, including two-component proteins, such as histidine kinases and response regulators, serine threonine kinases, sigma factors and their associated transcriptional factors, and other proteins with no homology to known proteins, have been identified (2,7,8,9,10,13,14,33,42,47). In this study we have focused on a putative 54 activator that may play an important role in M. xanthus developmental gene regulation.…”

Prokaryotic Development: Emerging Insights

“…H. Kaplan (University of Texas-Houston) has used lacZ fusions to genes induced early during development in screens for mutants. This approach initially uncovered a two-component system (SasS/ SasR) that senses and responds to A signal, a cell density signal composed of peptides and amino acids generated by extracellular M. xanthus proteases at the onset of development (35,129). A third component, SasN, inhibits SasS/SasR during growth, providing a nutritional status input that does not depend on cell density (128).…”