Isolation and characterization of the alpha and beta subunit genes of the high affinity receptor for Immunoglobin E
Witthuhn, Bruce A
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Allergic responses are mediated through the high affinity Fc receptor for immunoglobulin E (FceRI) which is expressed exclusively on mast cells and basophils. These responses occur when receptor-bound IgE molecules are crosslinked on the cell surface via an interaction with an antigen. The FceRI receptor is a heterotetrameric protein structure, composed of three distinct polypeptides - one alpha, one beta and two gamma subunits, The rat alpha and beta subunit genes have been cloned in this study in order to better understand their tissue-specific expression, The alpha subunit gene was found to span eight kilobase pairs of DNA. A construction consisting of the entire coding region and the 5'- and 3'- flanking regions was electroporated into the mouse mastocytoma cell line, P815, which does not express the endogenous genes for the alpha or beta subunits of the FceRI. The transcription of the exogenous rat alpha subunit gene was demonstrated by Northern blot and polymerase chain reaction analyses. These results suggest that the tissue-specific nature of expression is conserved across species lines. The beta subunit gene composed of seven exons and six introns spans nine kilobase pairs of DNA. Analysis of the 5'-flanking region identifies putative transcriptional cis-control elements, including PyPyCAPyPyPyPy, TATA and CAAT consensus sequences. Also identified are the consensus binding sites for the GATA transcription factors, as well as potential interferon-y regulated consensus elements, Also noted are an 19 bp homopurine-homopyrimidine direct repeat and an 11 bp homopurinehomopyrimidine inverted repeat embedded in a 123 bp homopurinehomopyrimidine region. These elements may contribute in the tissuespecific expression of this gene. Alternative RNA processing involving exon three may explain the origin of the two previously reported beta subunit transcripts. The close correspondence of the structure of the carboxy-terminal coding exon to a recently identified functional cytoplasmic domain is noted for the full-length transcript. Some correlations of predicted structural features of the polypeptide to the other exons are also apparent.