Coupling of multicellular morphogenesis and cellular differentiation by an unusual hybrid histidine protein kinase in Myxococcus xanthus

We describe an unusual hybrid histidine protein kinase, which is important for spatially coupling cell aggregation and sporulation during fruiting body formation in Myxococcus xanthus. A rodK mutant makes abnormal fruiting bodies and spores develop outside the fruiting bodies. RodK is a soluble, cytoplasmic protein, which contains an N-terminal sensor domain, a histidine protein kinase domain and three receiver domains. In vitro phosphorylation assays showed that RodK possesses kinase activity. Kinase activity is essential for RodK function in vivo. RodK is present in vegetative cells and remains present until the late aggregation stage, after which the level decreases in a manner that depends on the intercellular A-signal. Genetic evidence suggests that RodK may regulate multiple temporally separated events during fruiting body formation including stimulation of early developmental gene expression, inhibition of A-signal production and inhibition of the intercellular C-signal transduction pathway. We speculate that RodK undergoes a change in activity during development, which is reflected in changes in phosphotransfer to the receiver domains.