Distinct forms of the beta subunit of GTP-binding regulatory proteins identified by molecular cloning.

Abstract

Two distinct .beta. subunits of guanine nucleotide-binding regulatory proteins have been identified by cDNA cloning and are referred to as .beta.1 and .beta.2 subunits. The bovine transducin .beta. subunit (.beta.1) has been cloned previously. We have now isolated and analyzed cDNA clones that encode the .beta.2 subunit from bovine adrenal, bovine brain, and a human myeloid leukemia cell line, HL-60. The 340-residue Mr 37,329 .beta.2 protein is 90% identical with .beta.1 in predicted amino acid sequence, and it is also organized as a series of repetitive homologous segments. The major mRNA that encodes the bovine .beta.2 subunits is 1.7 kilobases in length. It is expressed at lower levels than .beta.1 subunit mRNA in all tissues examined. The .beta.1 and .beta.2 messages are expressed in cloned human cell lines. Hybridization of cDNA probes to bovine DNA showed that .beta.1 and .beta.2 are encoded by separate genes. The amino acid sequences for the bovine and human .beta.2 subunit are identical, as are the amino acid sequences for the bovine and human .beta.1 subunit. This evolutionary conservation suggests that the two .beta. subunits have different roles in the signal transduction process.