Characterization and expression of an Fc gamma receptor cDNA cloned from rat natural killer cells.

Abstract

A cDNA clone for an IgG-binding Fc receptor, rtFc.gamma.R.alpha., of the rat natural killer cell line CRNK-16 is characterized here. This clone encodes an Fc.gamma. receptor as shown by the ability of cDNA-transfected COS cells to rosette IgG-coated sheep erythrocytes. The rtFc.gamma.R.alpha. is exceptionally homologous to the mouse moFc.gamma.R.alpha., with 77% protein sequence identity and 71% nucleic acid identity overall. The transmembrane region of the rtFc.gamma.R.alpha. contains the sequence Leu-Phe-Ala-Val-Asp-Thr-Gly-Leu, which is present in the membrane sequences of four other Fc receptors including mouse Fc.gamma.R.alpha., human Fc.gamma.RIII-2, and the Fc.epsilon.R.alpha. subunits of the rat and human high-affinity IgE-binding receptors. Also, the rtFc.gamma.R.alpha. cytoplasmic domain exhibits specific homology to other receptors derived from natural killer cells, human Fc.gamma.RIII-2 and mouse Fc.gamma.R.alpha.. However, the rtFc.gamma.R.alpha. cDNA clone is complementary to at least two different-sized mRNAs expressed by CRNK-16 cells, containing the single Fc.gamma.R-related mRNA species expressed by human and mouse natural killer cells. These rat mRNAs are homologous to both the 5'' and the 3'' end of the cDNA clone, suggesting that they may be (i) splice variants of one transcript or (ii) products of different but highly related genes.