A cDNA presumptively coding for the .alpha. subunit of the receptor with high affinity for immunoglobulin E

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Abstract
Rat mast cells and a neoplastic analogue such as rat basophilic leukemia (RBL) cells have receptors that have exceptionally high affinity for immunoglobuoin E (IgE). When aggregated, these receptors induce cellular degrandulation. The .alpha. chain of the receptor contains the binding site for IgE; the function(s) of the noncovalently associated .beta. and .gamma. chains is (are) still undefined. Using a cDNA library constructed from the mRNA of RBL cells, we have isolated a cDNA clone whose sequence predicts a putative 23-residue signal peptide, followed by a sequence that accurately predicts the amino acid composition, the peptide molecular weight, and six peptide sequences (encompassing 59 residues or 26% of the total number) determined for the .alpha. chain by direct analysis. These findings provide strong evidence that the cDNA codes for the .alpha. chain, even though expression has not been unambiguously achieved. The sequence suggests that the .alpha. chain contains a 180-residue extracellular portion with two homologous domains of approximately 35 residues, a 20-residue transmembrane segment containing an aspartic acid, and a 27-residue cytoplasmic portion containing 9 basic amino acids. The sequence shows no homology with the low-affinity receptor for IgE from lymphocytes but over 30% homology with an Fc.gamma. receptor.