IDENTIFICATION OF FUNCTIONAL DOMAINS OF INTERLEUKIN-3 BY CONSTRUCTIONOF PRIMATE INTERSPECIES CHIMERA

Interleukin-3 (IL-3) is involved in regulation of proliferation and di fferentiation of multipotent hemopoietic cells and stimulates the prod uction of most blood cell types. The observed functional specificity a cross species concurs with an extreme rate of IL-3 amino acid substitu tions during mammalian evolution. Tamarin IL-3 exhibited 70.5% sequenc e identity with human IL-3 and was severely impaired in supporting pro liferation of human IL-S-dependent cells. In contrast, chimpanzee IL-3 displayed high amino acid sequence homology (98.5%) and could substit ute for human IL-3. A panel of interspecies chimera between the chimpa nzee and tamarin IL-3 genes has been constructed and expressed in Esch erichia coli and eukaryotic cells to investigate the role of substitut ions in different protein domains on the functional species specificit y. Our analyses show that substitutions at residues encoded by the fir st two exons appear crucial in the functional species specificity, whe reas C-terminal alterations show only moderate effects.