We have previously isolated a novel protein with two C2-like domains from rat brain, and named it B/K based on its predominant expression in the brain and kidney. We now report isolation of a human brain cDNA encoding B/K protein, and its mRNA distribution in various human tissues. The 1.5 kb human B/K cDNA clone exhibits 89% and 97% identities with rat B/K in the sequences of nucleotide and amino acid, respectively. Human B/K isoform encoding a 474 amino-acid protein shows structural features that are in common with rat counterpart including two C2 domains in its C-terminal region, three consensus sequences for protein kinase A, the absence of transmembrane region, and conservation of N-terminal cysteine cluster. On northern and dot blot analyses, a human B/K cDNA probe hybridized to a 3.0 kb B/K transcript abundantly present in human brain, kidney, and prostate. Among the brain regions, strong signals were observed in the frontal and temporal lobes, hippocampus, hypothalamus, amygdala, substantia nigra, and pituitary. A high degree of conservation in the primary structure and the pattern of mRNA distribution between rat and human B/K suggest that B/K proteins play a specific role in the area where they are expressed.

Keywords: Protein kinase A, double C2 domain, calcium, cysteine cluster