Inositol Phospholipid-Specific Phospholipase C: Complete cDNA and Protein Sequences and Sequence Homology to Tyrosine Kinase-Related Oncogene Products

Antibodies against an inositol phospholipid-specific phospholipase C purified from bovine brain were used to screen rat brain λ gt11 expression cDNA libraries. Complete sequences of three cDNA inserts yielded a cumulative sequence of 5106 base pairs. The deduced protein had 1289 amino acids with a calculated molecular weight of 148,431. The determination of an open reading frame was aided by the amino acid sequences of 21 tryptic peptides isolated from bovine brain phospholipase C. Only 9 residues of a total of 140 amino acid residues determined for the bovine enzyme were different from those deduced from the rat cDNA. Two regions of phospholipase C (amino acid residues 555-598 and 668-705) exhibited significant amino acid similarities to the products of various tyrosine kinase-related oncogenes (yes, src, fgr, abl, fps, fes, and tck). The homologous domain was located in the region that is not essential for the protein-tyrosine kinase activity but is likely to be involved in an interaction with cellular components that modulate kinase function. Therefore, this unexpected similarity raises the possibility that the 148-kDa phospholipase C and cytoplasmic tyrosine kinases are modulated by common cellular component(s).