RNA from rat hepatoma cells can activate phenylalanine hydroxylase gene of mouse erythroleukemia cells.

Mouse erythroleukemia (MEL) cells do not synthesize any detectable level of phenylalanine hydroxylase and thus do not grow in Tyr- medium. Rat hepatoma cells that constitutively express phenylalanine hydroxylase were treated prior to fusion with MEL cells with biochemical inhibitors to inactivate different macromolecular components of the cells, and the fusion products were selected in Tyr- medium. Continuously growing populations of cells resembling the parental MEL cells and expressing mouse phenylalanine hydroxylase were obtained only when rat hepatoma cells treated with mitomycin or iodoacetamide, which inactivate DNA and SH proteins, respectively, were fused with MEL cells. Fusion of MEL cells with UV-treated rat hepatoma cells did not result in the activation of the mouse phenylalanine hydroxylase gene. UV treatment damages both DNA and RNA. These data suggested that RNA was involved in the regulation of phenylalanine hydroxylase gene. Additional evidence for the role of RNA in the phenylalanine hydroxylase gene regulation was obtained from RNA transfection studies. RNA only from cells which express phenylalanine hydroxylase, such as rat hepatoma cells and MEL cybrids, when introduced into MEL cells by the CaPO4 coprecipitation method, resulted in the permanent activation of the mouse phenylalanine hydroxylase gene.