G protein diversity: a distinct class of alpha subunits is present in vertebrates and invertebrates

Proc Natl Acad Sci U S A. 1990 Dec;87(23):9113-7. doi: 10.1073/pnas.87.23.9113.


Heterotrimeric guanine nucleotide-binding proteins (G proteins) are integral to the signal transduction pathways that mediate the cell's response to many hormones, neuromodulators, and a variety of other ligands. While many signaling processes are guanine nucleotide dependent, the precise coupling between a variety of receptors, G proteins, and effectors remains obscure. We found that the family of genes that encode the alpha subunits of heterotrimeric G proteins is much larger than had previously been supposed. These novel alpha subunits could account for some of the diverse activities attributed to G proteins. We have now obtained cDNA clones encoding two murine alpha subunits, G alpha q and G alpha 11, that are 88% identical. They lack the site that is ordinarily modified by pertussis toxin and their sequences vary from the canonical Gly-Ala-Gly-Glu-Ser (GAGES) amino acid sequence found in most other G protein alpha subunits. Multiple mRNAs as large as 7.5 kilobases hybridize to G alpha q specific probes and are expressed at various levels in many different tissues. G alpha 11 is encoded by a single 4.0-kilobase message which is expressed ubiquitously. Amino acid sequence comparisons suggest that G alpha q and G alpha 11 represent a third class of alpha subunits. A member of this class was found in Drosophila melanogaster. This alpha subunit, DG alpha q, is 76% identical to G alpha q. The presence of the Gq class in both vertebrates and invertebrates points to a role that is central to signal transduction in multicellular organisms. We suggest that these alpha subunits may be involved in pertussis toxin-insensitive pathways coupled to phospholipase C.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • Biological Evolution
  • Drosophila / genetics
  • GTP-Binding Proteins / genetics*
  • Genetic Variation*
  • Invertebrates / genetics*
  • Macromolecular Substances
  • Molecular Sequence Data
  • Multigene Family*
  • Oligonucleotide Probes
  • Polymerase Chain Reaction
  • Sequence Homology, Nucleic Acid
  • Vertebrates / genetics*


  • Macromolecular Substances
  • Oligonucleotide Probes
  • GTP-Binding Proteins

Associated data

  • GENBANK/M55411
  • GENBANK/M55412