Classification of tyrosine kinases from Dictyostelium discoideum with two distinct, complete or incomplete catalytic domains

Two new kinases of Dictyostelium discoideum were identified by screening of a (lambda)gt11 expression library with a phosphotyrosine specific antibody. Amino-acid sequences derived from cDNA and genomic clones indicate that DPYK3 is a protein of 150 kDa and DPYK4, a protein of 75 kDa. The C-terminal fragments of each protein were produced in Escherichia coli and shown to be autocatalytically phosphorylated at tyrosine residues. A common feature of these kinases is the presence of two different sequence stretches in tandem that are related to kinase catalytic domains. The sequence relationships of DPYK3 and 4 to other protein kinases, and the positions of their catalytic domain sequences within the phylogenetic tree of protein kinases were analysed. Domains I of both kinases and domain II of DPYK3 constitute, together with the catalytic domains of two previously described tyrosine kinases of D. discoideum, a branch of their own, separate from the tyrosine kinase domains in sensu strictu. Domain II in DPYK4 is found on a different branch close to serine/threonine kinases.