Heterotrimeric guanosine triphosphate (GTP)-binding proteins (G proteins) may participate in membrane traffic events. A complementary DNA (cDNA) was isolated from a mouse pituitary cDNA library that corresponded to an alternatively spliced form of the gene encoding the G protein alpha subunit G alphai2. The cDNA was identical to that encoding G alphai2 except that the region encoding for the carboxyl-terminal 24 amino acids was replaced by a longer region encoding 35 amino acids that have no sequence similarity with G alphai2 or other members of the G protein family. This alternative spliced product and the corresponding protein (sGi2) were present in several tissues. Specific antibodies revealed that sG (i2) was localized in the Golgi apparatus, suggesting a role in membrane transport. Thus, alternative splicing may generate from a single gene two G protein alpha subunits with differential cellular localization and function.