Src proteins/ genes: from sponges to mammals

The genome of marine sponge Suberites domuncula, a member of the most ancient and most simple metazoan phylum Porifera, encodes at least five genes for Src-type proteins, more than, i.e., Caenorhabditis elegans or Drosophila melanogaster (two in each). Three proteins, SRC1SD, SRC2SD and SRC3SD, were fully characterized. The overall homology (identity+similarity) among the three S. domuncula Srcs (68–71%) is much lower than the sequence conservation between orthologous Src proteins from freshwater sponges (82–85%). It is therefore very likely that several src genes/proteins were already present in the genome of Urmetazoa, the hypothetical metazoan ancestor.