The present invention provides a chimera gene as constructed by fusing the gene for the extracelluar region of human growth hormone receptor with the genes for the transmembrane and cytoplasmic regions of thrombopoietin receptor, an expression plasmid for the said gene and animal cells capable of expressing the protein encoded by the said gene.
The human-growth-hormone dependent animal cell line transformed with an expression plasmid for the said gene are useful in screening hormones which show affinity for the chimera receptor, as well as their agonists and antagonists.