Light-induced interaction of putative phosducin with Gβγ-subunits of G-protein in the ciliate Blepharisma japonicum

Immunoblot of whole-cell lysate from Blepharisma japonicum with a polyclonal antibody raised against the rat phosducin display one major protein band of molecular weight of 28 kDa. Immunoprecipitation of detected phosducin immunoanalogue from lysate of dark- and light-adapted ciliates with the anti-phosducin antibody and subsequent analysis of the precipitated protein with a monoclonal antibody raised against phosphoserine residues revealed also the presence of a 28 kDa protein phosphorylated on a serine residues. This phosphoprotein exists in a highly phosphorylated form in ciliates adapted to darkness and its dephosphorylation occurs in illuminated cells. An immunoblot assay of the precipitated phosducin-related protein with a rabbit polyclonal antibody directed against beta-subunit of G-protein showed one major protein band of molecular weight of about 34 kDa in lysate obtained from ciliates exposed to light. In addition, based on partial cloning of the putative ciliate phosducin nucleotide sequence homology to the phosducin belonging to the subgroup 1 of phosducin protein family was deduced. The results obtained in this study confirm the previously reported hypothesis that in the ciliated protist Blepharisma japonicum phosducin does exist and resembles that observed in a wide variety of higher eukaryotes and also in some microorganisms.