Molecular cloning and structure of the human interleukin-5 gene

We isolated the chromosomal gene for human interleukin-5 (IL-5) from human genomic libraries using a cloned human IL-5 cDNA as probe. Nucleotide sequence determination of the IL-5 gene and its flanking regions showed that the gene consisted of four exons and three introns. TATA-like and CAAT-like sequences reside 26 and 73 base pairs, respectively, upstream of the transcription initiation site identified by S1 mapping analysis. The 5'-flanking region of the IL-5 gene has sequences homologous with those of the corresponding regions of the genes for human granulocyte/macrophage colony-stimulating factor, murine IL-4, human interferon-gamma, and human IL-2. The intron-exon organization and location of the cysteine residue suggest that the IL-5 gene is phylogenetically related to the genes for the granulocyte/macrophage colony-stimulating factor, IL-4, and IL-2, although their amino acid sequences are not significantly conserved.