PHYLOGENETIC RELATIONSHIP OF ADHESION PROTEINS AND UBIQUITIN FROM THEMARINE SPONGE GEODIA-CYDONIUM

The shift from unicellular life to multicellular, integrated organisms has been accompanied by the acquisition of adhesion proteins. Recentl y we succeeded to clone some genes coding for such proteins from the l owest multicellular animals, the marine sponges (model: the siliceous sponge Geodia cydonium). G. cydonium contains e.g. several lectins; cD NA for two of them (termed LECT-1 and LECT-2) was cloned. Both lectins have a framework sequence of 38 conserved amino acids which are chara cteristic for the carbohydrate binding site of vertebrate S-type lecti ns. Next, we have isolated and characterized a cDNA coding for a recep tor tyrosine kinase of class II (GCTK). The deduced aa sequence shows two characteristic domains; (i) the tyrosine kinase domain and (ii) an immunoglobulin-like domain. The latter part shows high homology to th e vertebrate type immunoglobulin domain. This result together with the lectin data demonstrates that binding domains of such adhesion protei ns are not recent achievements of higher animals but exist already in animals (sponges) which have diverged from other organisms about 800 m illion years ago. Ubiquitin is a 76-residue protein which is highly co nserved among eukaryotes. Sponge cDNA for poly-ubiquitin was cloned; t he sponge gene (GCUBI) contains six repeats, GCUBI-1 to GCUBI-6. On th e nt level the sequences of the six repeats differ considerably. Mutat ional analysis suggests that the sponge polyubiquitin gene evolved fro m an ancestral monoubiquitin gene by gene duplication and successive t andem duplications. The first event, duplication of the monoubiquitin gene, happened some 110 millions years ago. These data support the vie w that the kingdom Animalia is monophyletic.