 Overexpression of HBO1 has been shown to induce DNA-replication. To determine whether E1A uses HBO1 in inducing re-replication by stimulating the HBO1 HAT activity, the investigators will infect S phase enriched cells isolated by double thymidine block with Ad viruses expressing the WT or mutant E1A proteins along with Ad vectors expressing HBO1 variants e.g. HAT inactive, allow the infection to proceed as needed then quantify the population of cells containing 4N DNA content using flow cytometer. If E1A simulated HBO1 HAT activity is important for re-replication HAT defective HBO1 mutants will not induce re-replication even in the presence of E1A. E1A mutants that cannot bind to HBO1 will also show a similar phenotype. 