Methylation of human ornithine decarboxylase gene before transfection abolishes its transient expression in Chinese hamster ovary cells

Different methylations of cloned human ornithine decarboxylase gene with restriction methylases in vitro before transfection greatly reduced the transient expression of ODC in Chinese hamster ovary cells. Single methylation of the gene with Hpa II (CCGG) methylase decreased the transiently expressed peak activity by about 50%, single methylation with Hha I (CCGG) methylase by about 80% whilst a double methylation at both Hpa II and Hha I restriction sites virtually abolished any transiently expressed ornithine decarboxylase activity. These results together with our earlier circumventing evidence indicate that the expression of mammalian ornithine decarboxylase is critically influenced by the methylation state of the gene.