Multiple phosphorylation of membrane-associated calcium-dependent protein serine/threonine kinase in Streptomyces fradiae

In Streptomyces fradiae, calcium ions induce alterations in intensity and s pecificity of the secondary metabolism and stimulate aerial mycelium format ion and sporulation. Using in vitro labeling, we demonstrate that in S. fra diae in the late exponential growth phosphorylation of 65-kDa membrane-asso ciated protein is also influenced by Ca2+ added exogenously. Calcium ions a t physiological concentration stimulate intensive Ca2+-dependent phosphoryl ation of 65-kDa protein at multiple sites on serine, threonine, and tyrosin e residues. Assay of protein kinases in situ demonstrated in the fraction o f membrane-associated proteins the presence of two autophosphorylating prot ein serine/threonine kinases with molecular masses of 127 kDa and 65 kDa. A utophosphorylation of both proteins is also Ca2+-dependent. (C) 2001 Publis hed by Elsevier Science B.V. on behalf of the Federation of European Microb iological Societies.