ALTERNATIVE MESSENGER-RNA SPLICING GENERATES TISSUE-SPECIFIC ISOFORMSOF 116-KDA POLYPEPTIDE OF VACUOLAR PROTON PUMP

The cDNA encoding the 116-kDa polypeptide of the bovine brain vacuolar -type proton translocating ATPases has been cloned and sequenced. One of five clones differed from all others in that it contained an 18-bas e pair deletion within the coding region, whereas it was identical to the other clones in overlapping coding and noncoding regions, indicati ng that this heterogeneity arises through an alternative splicing mech anism. By conventional Northern analysis, only one 4.1-kilobase mRNA w as identified in bovine brain, heart, kidney, liver, and spleen. Howev er, a polymerase chain reaction-based analysis revealed two species of mRNA with a tissue specific distribution. Type I, containing the 18-b ase pair insert, was found in brain, whereas the truncated (Type II) f orm was found in all tissues examined. Similar tissue distributions of rat mRNA were observed. The deletion site accounting for this variabi lity occurs within a predicted protease sensitivity motif (PEST site), suggesting that differences in the biological half-life of the two 11 6-kDa isoforms may exist.