EARLY EVOLUTION OF METAZOAN SERINE THREONINE AND TYROSINE KINASES - IDENTIFICATION OF SELECTED KINASES IN MARINE SPONGES/

The phylum Porifera (sponges) was the first to diverge from the common ancestor of the Metazoa. In this study, six cDNAs coding for protein- serine/threonine kinases (PS/TKs) are presented; they have been isolat ed from libraries obtained from the demosponges Geodia cydonium and Su berites domuncula and from the calcareous sponge Sycon raphanus. Seque nce alignments of the catalytic domains revealed that two major famili es of PS/TK, the ''conventional'' (Ca2+-dependent) protein kinase C (P KC), the cPKC subfamily, as well as the ''novel'' (Ca2+-independent) P KC (nPKC), form two separate clusters. In each cluster, the sequence f rom S. raphanus diverges first. To approach the question about the ori gin of protein-tyrosine kinases (PTK), which are found only in Metazoa , we analyzed two additional PS/TKs which have been cloned from S. dom uncula: the stress-responsive protein kinase (KRS_SD) and the protein- kinase-C-related kinase (PRK_SD). The construction of the phylogenetic tree, comprising the eight PS/TKs and the PTK cloned previously from G. cydonium, revealed that the PTK derived from the branch including t he KRS_SD kinase. These data facilitate the first molecular approach t o elucidate the origin of metazoan PTK within the PS/TK superfamily.