Molecular cloning of β3 subunit, a third form of the G protein β-subunit polypeptide

M. A. Levine, P. M. Smallwood, P. T. Moen, L. J. Helman, T. G. Ahn

Research output: Contribution to journalArticlepeer-review

119 Scopus citations


The signal-transducing guanine nucleotide-binding regulatory (G) proteins are heterotrimers composed of three subunits - α, β, and γ. Although multiple distinctive forms of the α subunit have been described, only two forms of the β subunits of the G proteins have been identified. To investigate further the structural diversity of the β subunits, we screened bovine and human retina cDNA libraries and isolated clones encoding three distinct types of G protein β subunit. One form was identical to previously isolated β1-subunit cDNA clones that encode the 36-kDa form of the β subunit, whereas a second form was identical to previously described β2 cDNAs that encode the 35-kDa β isoform. In addition, we identified another species, designated β3 subunit, which encodes a third distinct form of the β subunit. The β3-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 M(r) of 37,221. The amino acid sequences of the three β subunits are closely related: 83% identity between β1 and β3 subunits and 81% identity between β2 and β3 subunits. By contrast, the 3'-untranslated regions of the three cDNAs show no significant homology. Our data support the hypothesis that a family of β-subunit poplypeptides exists and extend understanding of β-subunit structure.

Original languageEnglish (US)
Pages (from-to)2329-2333
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number6
StatePublished - 1990
Externally publishedYes


  • molecular cloning
  • signal transduction

ASJC Scopus subject areas

  • General


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