Phosphoinositide-specific phospholipase C(PLC) is a crucial enzyme in transmembrane signaling. Six mammalian PLC isozymes including PLC-β1, PLC-β2, PLC-γ1, PLC-γ2, PLC-δ1, and PLC-δ2 have been identified at both protein and DNA levels.
All mammalian PLC sequences contain highly conserved two domains, designated as X and Y. Degenerate PCR primers corresponding to consensus sequences of X and Y domains were synthesized to probe new type of PLC-β family. A PCR product from a rat brain cDNA library that contain a PLC-like sequence distinct from those of the corresponding regions of known PLC isozymes was obtained. The cloned PCR product was used as a probe to screen rat libraries. Two different cDNA clones and a genomic clone were isolated from FRTL-5 cDNA, brain cDNA, and genomic libraries. The whole cDNA and the region corresponding to the amino terminal part of the new PLC gene were sequenced. The two cDNA sequences were identical except that the 201 nucleotide (67 amino acids) long DNA fragment in the shorter one was deleted from the larger one. The larger cDNA consists of 4,176 nucleotides and contains a single reading frame that encodes 1,234 amino acids. The open reading frame of the shorter one was not shifted. The deduced amino acid sequence of the new PLC cDNA was similar in primary structure and overall structural organization to known PLC-β isoforms. The amino acid sequence of the new PLC was more similar to that of PLC-β1 than to that of PLC-β2. The new PLC was named, PLC-β3.
Antibodies against PLC-β3 were raised using four different peptides corresponding to different parts of the PLC-β3 amino acid. Immunoblotting assay showed that a PLC-β3 like protein is present in various rat tissues. It was abundant in parotid gland, brain, and liver. Relatively small anount of PLC-β3 was also present in uterus, lung, heart, adrenal gland, and ovary tissues. However, levels of PLC-β3 presenting various tissues of rat were approximately 100 times less than PLC-β1.