ABSTRACTTo understand better the regulation of interleukin-5 receptor α-subunit (IL-5Rα) expression, we have isolated the genomic clones of mouse IL-5Rα (mIL-5Rα) and analyzed the structure of the gene. The gene spans more than 35 kb and is composed of 11 exons. We found that two mRNAs encoding secreted forms of mIL-5Rα result from differential splicing events. We identified the transcriptional start site by primer extension analysis of mIL-5Rα mRNA. Nucleotide sequence of the 5′-flanking region contains potential binding sites for transcription factor Ap1, AP-1, GATA-1, and PU.1. About 260 bp sequence of the 5′-flanking region exhibited promoter activity when it was linked to a promoterless bacterial chloramphenicol acetyltransferase (CAT) gene. The promoter activity was seen not only in the IL-5-dependent pre-B-cell line Y16, but also in fibroblast cell line NIH-3T3. Comparison of the exon-intron boundaries of mIL-5Rα genes with those of other members of the cytokine receptor family reveals a conserved evolutionary structure. By fluorescencein situhybridization analysis, the mIL-5Rα gene has been assigned to
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