Molecular cloning of beta 3 subunit, a third form of the G protein beta-subunit polypeptide.
The signal-transducing guanine nucleotide-binding regulatory (G) proteins are heterotrimers composed of three subunits--alpha, beta, and gamma. Although multiple distinctive forms of the alpha subunit have been described, only two forms of the beta subunits of the G proteins have been identified. To investigate further the structural diversity of the beta subunits, we screened bovine and human retina cDNA libraries and isolated clones encoding three distinct types of G protein beta subunit. One form was identical to previously isolated beta 1-subunit cDNA clones that encode the 36-kDa form of the beta subunit, whereas a second form was identical to previously described beta 2 cDNAs that encode the 35-kDa beta isoform. In addition, we identified another species, designated beta 3 subunit, which encodes a third distinct form of the beta subunit. The beta 3-subunit cDNA corresponds to a 2.0-kilobase mRNA expressed in all tissues and clonal cell lines examined. Nucleotide sequence analysis indicates that the encoded peptide consists of 340-amino acid residues with a Mr of 37,221. The amino acid sequences of the three beta subunits are closely related: 83% identity between beta 1 and beta 3 subunits and 81% identity between beta 2 and beta 3 subunits. By contrast, the 3'-untranslated regions of the three cDNAs show no significant homology. Our data support the hypothesis that a family of beta-subunit polypeptides exists and extend understanding of beta-subunit structure.
Levine
M A
MA
Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205.
Smallwood
P M
PM
Moen
P T
PT
Helman
L J
LJ
Ahn
T G
TG
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002417:Cattle; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics; D019204:GTP-Binding Proteins / Q000235:genetics*; D015723:Gene Library; D006801:Humans; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D009693:Nucleic Acid Hybridization; D015345:Oligonucleotide Probes; D012333:RNA, Messenger / Q000235:genetics; D012160:Retina / Q000378:metabolism; D012689:Sequence Homology, Nucleic Acid
D046911:Macromolecular Substances; D015345:Oligonucleotide Probes; D012333:RNA, Messenger; D004247:DNA; D019204:GTP-Binding Proteins