2 FORMS OF PHOSPHOLIPASE C-BETA-1 GENERATED BY ALTERNATIVE SPLICING

Phospholipase C-beta 1 (PLC-beta 1) exists as two immunologically indi stinguishable polypeptides of 150 and 140 kDa and is encoded in rat br ain by two distinct transcripts of 5.4 and 7.2 kilobases (kb). cDNA co rresponding to the entire 5.4-kb transcript as reported previously rev eals an open reading frame that is capable of coding a 1216-amino acid polypeptide (Suh, P. G., Ryu, S. H., Moon, K. H., Suh, H. W., and Rhe e, S. G. (1988) Cell 54, 161-169). We have now isolated cDNAs correspo nding to the entire 7.2-kb transcript from a rat brain cDNA library. T he 7.2-kb transcript differs from the previously reported 5.4-kb trans cript by possessing both an additional 118 nucleotides located near th e end of the coding sequence and a 1738-nucleotide extension of the 3' -flanking region. The presence of the 118-nucleotide insert in the cum ulative 7.2-kb sequence gives rise to an open reading frame that is ca pable of coding a 1173-amino acid polypeptide (PLC-beta 1b), the carbo xyl terminal sequence of which differs from that of the 1216-amino aci d polypeptide (PLC-beta 1a) derived from the 5.4-kb transcript. Antibo dies were raised against synthetic peptides corresponding to the carbo xyl-terminal portions of PLC- beta 1a and PLC-beta 1b. Immunoblot anal ysis with these isozyme specific antibodies revealed that both PLC-bet a 1a and PLC-beta 1b are expressed in rat brain and C(6)Bu-1 glioma ce lls and that PLC-beta 1a and PLC-beta 1b correspond to the previously identified 150- and 140-kDa PLC-beta 1 enzymes, respectively. Analysis of PLC-beta 1 genomic DNA indicates that PLC-beta 1a and PLC-beta 1b are derived from a single gene by alternative RNA splicing.