Pkg2, a novel transmembrane protein Ser/Thr kinase of Streptomyces granaticolor

A 4.2-kb SphI-BamHI fragment of chromosomal DNA from Streptomyces granatico lor was cloned and shown to encode a protein,vith significant sequence simi larity to the eukaryotic protein serine/threonine kinases, It consists of 7 01 amino acids and in the N-terminal part contains all conserved catalytic domains of protein kinases. The C-terminal domain of Pkg2 contains seven ta ndem repeats of 11 or 12 amino acids with similarity to the tryptopban-dock ing motif known to stabilize a symmetrical three-dimensional structure call ed a propeller structure. The pkg2 gene was overexpressed in Escherichia co li, and the gene product (Pkg2) has been found to be autophosphorylated at serine and threonine residues. The N- and C-terminal parts of Pkg2 are sepa rated with a hydrophobic stretch of 21 amino acids which translocated a Pho A fusion protein into the periplasm. Thus, Pkg2 is the first transmembrane protein serine/threonine kinase described for streptomycetes, Replacement o f the pkg2 gene by the spectinomycin resistance gene resulted in changes in the morphology of aerial hyphae.