CLONING AND SEQUENCING OF PARAFUSIN, A CALCIUM-DEPENDENT EXOCYTOSIS-RELATED PHOSPHOGLYCOPROTEIN

A cDNA for parafusin, an evolutionarily conserved phosphoglycoprotein involved in exocytosis, has been cloned and sequenced from a unicellul ar eukaryote, Paramecium tetraurelia. A Paramecium cDNA library was sc reened with an oligonucleotide probe synthesized to an internal amino acid sequence of isolated parafusin. The insert was 3 kb long with an open reading frame of 1.75 kb. Data base searches of the deduced amino acid sequence showed that Paramecium parafusin had a 50.7% sequence i dentity to rabbit muscle phosphoglucomutase, although no detectable ph osphoglucomutase activity has been detected in isolated parafusin. The deduced parafusin amino acid sequence had four inserts and two deleti ons, which might confer on the protein Specific functions in signal tr ansduction events related to exocytosis. Furthermore, searches for pot ential phosphorylation sites showed the presence of a protein kinase C site (KDFSFR) specific to parafusin. Southern blot analysis with prob es specific for parafusin and phosphoglucomutase suggested that these proteins were products of different genes. We propose that parafusin a nd phosphoglucomutase are members of a superfamily that conserve homol ogies important for the tertiary structure of the molecules.