Abstract: The molecular cloning of humansyk DNA, compositions containing same and uses thereof are disclosed.

Abstract: Methods and compositions are provided for modified cells, where a chimeric protein consisting of a ligand binding domain fused to an action domain is employed which initiates a signal which activates a biological process: transcription of at least one gene, usually a second construct introduced into the host cells; exocytosis; or an extracellular process. The second construct optimally present provides for a promoter which responds to a transcriptional activation action domain to provide for transcription, when an appropriate ligand binds to the ligand binding domain. Exemplary of the system is the use of an FKBP/CD3.zeta. or transcription factor fusion protein, using dimeric FK506 or FK520 as the ligand and a promoter responsive to NF-AT or other transcription factor requiring two molecules for transcriptional activation.