MOLECULAR AND BIOCHEMICAL-CHARACTERIZATION OF A RECOMBINANT HUMAN PKC-DELTA FAMILY MEMBER

Two cDNA clones coding for the human protein kinase C-delta (PKC-delta ) were fortuitously isolated during the process of screening a human l ibrary for a cDNA clone of an unrelated protein, the nucleolar protein fibrillarin. The two human homologues have about 88% nucleotide seque nce identity to the rat and mouse PKC-delta cDNA clones. A comparison of the predicted amino acid sequences of the two human PKC-delta clone s with the rat and mouse homologues indicated a greater degree of sequ ence divergence (89-90% homology) compared to the high degree of seque nce conservation observed with other human PKC family members and thei r mammalian counterparts. Expression of the clones in the baculovirus insect-cell expression system indicated that both proteins exhibited p horbol ester binding activity, and were dependent upon phosphatidylser ine and diacylglycerol for maximal activation. Further characterizatio n of the properties of the human PKC-delta revealed substrate and lipi d dependencies distinct from other members of the protein kinase C fam ily; including PKC-deltas isolated from other species. The dissimilari ties in the predicted amino acid sequences between the human and other mammalian species could account in part for some of these observed bi ochemical differences.