Species Specificity of Human Interleukin - 3 Demonstrated by Cloning and Expression of the Homologous

To enable preclinical studies on homologous interleukin-3 (IL-3) in primate species, we isolated the gene encoding Rhesus monkey IL-3 (RhlL-3). The nucleotide sequence of the RhlL-3 gene displayed 92.9% homology with that of the human IL-3 (hlL-3) gene. The isolated RhlL-3 gene encodes a 143-amino acid (aa) precursor polypeptide, nine C-terminal residues shorter than the human protein. Protein homology was found to be 89.5% for the signal peptide (19 aa) and 80.5% for the mature protein (124 aa). Comparison of the human and RhlL-3 coding sequences showed that the majority of substitutions had occurred at amino acid replacement sites indicating a rapid evolution of the IL-3 protein. After expression of a genomic fragment in COS