Two-step transformation of rat 3Y1 cells by the adenovirus E1A and E1B genes.

The transformation of rodent cells by the adenovirus E1A and E1B genes was very efficient when these genes were physically linked. When they were cleaved, the transformation became very inefficient. To clarify this difference, the chimeric E1B genes in which either the adenovirus enhancer or the human beta-actin promoter was linked to the 5' side of the E1B gene were introduced into rat 3Y1 cells. The saturation density of these cell lines (eB or APrB) was similar to that of parental 3Y1 cells. When eB or APrB cell lines were supertransfected with the E1A gene, discrete dense foci were developed after 5-6 weeks, while the supertransfection of 3Y1 derivative cell lines, in which the enhancer-unlinked E1B gene was introduced, did not develop any dense foci. Analysis of the E1A and E1B transcripts in these cell lines indicated that the E1B gene is efficiently expressed in the presence of the E1A gene products if the enhancer is linked to the E1B gene and that an increased level of E1B proteins is required for an efficient expression of the E1A gene. These results indicated that E1A and E1B genes in separate pieces of DNA are capable of cooperatively transforming 3Y1 cells if appropriate cis-acting elements are attached and high-level expressions are achieved.