Cyclic AMP signaling is required for function of the N-terminal and CR1 domains of adenovirus E1A in Saccharomyces cerevisiae.

We have constructed yeast vectors in which derivatives of the adenovirus E1A gene are expressed from the GAL1 promoter. Cells expressing E1A289 grow poorly and accumulate cells with a 1C DNA content. Using a series of E1A deletion mutants, we have identified three regions within the E1A protein that are necessary for the G1 growth phenotype; each deletion partially relieves the growth defect. These deletions span residues 4-25, 38-60 and 140-186, which fall within the N-terminal, CR1 and CR3 domains of E1A respectively. Expression of the first 82 residues of E1A, spanning just the N-terminal and CR1 domains, strongly inhibits yeast cell growth in G1 showing that these domains can function independently of other domains of E1A. Using this strong growth inhibition, we isolated a yeast mutant in the net1 gene that conferred resistance to the expression of E1A1-82. The mutant was insensitive to expression of both E1A1-82 and full length E1A, but remained sensitive to the toxicity caused by over-expression of a Gal4p-VP16 fusion. Finally, we found that the function of E1A in yeast depends on the cyclic AMP signaling pathway, providing a striking parallel with the action of E1A at the c-fos promoter in mammalian cells. These results suggest that a genetic analysis of the yeast model system will provide relevant new insights into mechanisms of gene regulation by E1A proteins.