Identification of some of the brain Gn27 as the ral gene product. Comparison between the brain and platelet Gn-proteins.

Two major Gn-proteins, Gn27 and Gn26, were detected in the 100,000 x gav particulate fraction of rabbit and bovine brain. The Gn26 protein was also present in significant amounts (approximately 50% of total) in the brain supernatant fraction. An antiserum raised against recombinant simian ralA recognized a 27-kDa brain protein with the same apparent molecular mass as the Gn27 protein. In further analysis by two-dimensional polyacrylamide gel electrophoresis, the brain particulate Gn-proteins were resolved into 6 major forms, four of 27 kDa (Gn27a-d) and two of 26 kDa (Gn26a and Gn26b). Minor GTP-binding components were also observed at 25 kDa and 24 kDa. The ralA antibody reacted strongly with the brain Gn27b form and weakly with the Gn27a and Gn27c but not with Gn27d or any of the other Gn-proteins. In addition, comparison of human platelet and bovine brain particulate Gn-proteins by two-dimensional polyacrylamide gel electrophoresis demonstrated a tissue/cell-type specific expression of the various forms of Gn-proteins.