This action funds an NSF - Alfred P. Sloan Foundation Postdoctoral Research Fellowship in Molecular Evolution. Tradition holds that protein phosphorylation, a universal mechanism for cellular regulation, evolved independently in eukaryotes and prokaryotes. The existence of protein serine/threonine phosphatase in the prokaryotic archeon Sulfolobus solfataricus challenges this notion. This proposal seeks to characterize the phosphorylation network of S. Solfalarieus by identifying and characterizing its phosphoproteins.