Sequences of the bovine and yeast ADP-ribosylation factor and comparison to other GTP-binding proteins.

Abstract

The ADP-ribosylation factor (ARF) is a 21-kDa GTP-binding protein that serves as the cofactor in the cholera toxin-catalyzed activation of the stimulatory guanine nucleotide-binding protein of adenylate cyclase (Gs). An oligonucleotide probe based on the partial amino acid sequence was used to clone ARF from a bovine adrenal chromaffin cDNA library. The yeast (Saccharomyces cerevisiae) ARF gene was then cloned from a YCp50 genomic library by cross-species hybridization by using the coding region of the bovine gene. RNA gel blots of poly(A)+ RNA indicated that only one ARF message size (900 and 2000 base pairs) is present in yeast and cows, respectively. Comparison of the cDNA-derived amino acid sequences of ARF to other GTP-binding proteins reveals a structural relationship between ARF and the ras family of proteins. A slightly better structural relationship is detected when ARF is compared to the .alpha. subunits of the trimeric GTP-binding proteins, including Gs.alpha.. All of the biochemical characteristics of the purified ARF, including the lack of GTPase activity and the posttranslational myristoylation, are consistent with the derived sequences. Comparison of the ARF sequences to that of the chicken processed pseudogene (CPS-1), previously reported as a ras homologue, reveals that CPS-1 is actually an ARF-derived gene. These resutls demonstrate that ARF is a GTP-binding protein with structural features of both the ras and the trimeric GTP-binding protein families.