Structure and expression of the cAMP cell‐surface receptor

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Abstract
Using antibodies specific for the 3′, 5′-cyclic AMP (cAMP) cell surface receptor of Dictyostelium discoideum, we have screened γgtll expression libraries and isolated a series of cDNAs derived from cAMP receptor mRNA during early development. The identity of the cDNA clones was verified by multiple criteria: (1) β-galactosidase fusion proteins synthesized by isolated cDNA clones stain intensely with cAMP receptor directed antiserum, (2) these fusion proteins affinity purify antibodies specific for the cAMP receptor, (3) the cDNA probes hybridize to a 2 kb mRNA whose change in relative level of abundance during development parallels that of receptor mRNA as assayed by in vitro translation, (4) the 2 kb mRNA size equals that of receptor mRNA as determined by in vitro translation of size fractionated poly (A)+ RNA, and (5) RNA transcribed in vitro from cDNAs containing the entire protein-coding region produces a polypeptide by in vitro translation with an apparent molecular weight in close agreement with that of nascent cAMP receptor protein produced by in vitro translation of cellular RNA. The DNA sequence predicts an open reading frame of 392 amino acids. The deduced amino acid sequence contains seven domains enriched in hydrophobic residues. A model is proposed in which the cAMP cell-surface receptor traverses the lipid bilayer seven times in a pattern similar to that of other receptors, such as rhodopsin, which interact with G-proteins. The structural similarities suggest a gene family of related surface receptors from such evolutionarily diverse species as Dictyostelium, yeast, and mammals.