Falkor, a novel cell growth regulator isolated by a functional genetic screen.

A novel cell growth regulator, named Falkor, was identified using a functional approach to mammalian gene cloning, the Genetic Supressor Elements (GSE) method. In this screen, expression of the C-terminal domain of Falkor conferred cells with resistance to cisplatin-induced growth arrest. Expression of the C-terminus of Falkor, but not of the full-length protein, enhanced cell growth both following genotoxic stress and under normal conditions suggesting a general role for this protein in cell growth control. This effect of the C-terminus fragment was abrogated by over-expression of the full-length Falkor, suggesting that the fragment counteracts the function of the full-length protein. Falkor is encoded by a 2-kb mRNA which is present at different levels in various tissues, and is localized in the nucleus of cells. The C-terminal domain of Falkor, isolated from the GSE library, has significant homology to a known human and rat cell growth regulator, SM-20, and to the C. elegans protein EGL-9, recently shown to modify the Hypoxia Inducible Factor-1alpha. The homology suggests that these proteins share a functional domain that is conserved among a family of growth regulation proteins.