Molecular cloning of a human immunoglobulin G Fc receptor.

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Abstract
Human IgG Fc receptor (Fc.gamma.R) cDNA clones were isolated by cross-species hybridization by probing cDNA libraries with the low-affinity Fc.gamma.R .beta.1 cDNA clone from mouse as well as a pool of oligonucleotides constructed from the nucleotide sequence of this Fc.gamma.R. Three cDNA clones were isoalted and analysis of the predicted amino acid sequence indicated that the human Fc.gamma.R protein is synthesized with a 34-amino acid leader and the mature protein is composed of 281 amino acids. The extracellular region of this Fc.gamma.R was divided into two domains, which were very similar to each other and to the corresponding regions of both mouse .alpha. and .beta. Fc.gamma.Rs and showed a clear relationship to immunoglobulin variable regions. One possible N-linked glycosylation site was found in each of the extracellular domains. The human Fc.gamma.R leader sequence was shown to be similar to the mouse .alpha. Fc.gamma.R leader sequence, but the transmembrane region was most similar to the mouse .beta.1 Fc.gamma.R. The intracellular domain of the human Fc.gamma.R was surprisingly different from both mouse Fc.gamma.Rs. RNA blot analysis of human cells demonstrated two transcripts (2.5 and 1.5 kilobases) that arise by use of different adenylylation signals. The cellular expression of these transcripts suggests that they encode the low-affinity p40 Fc.gamma.R protein.