INDEPENDENT TRANSFORMATION ACTIVITY BY ADENOVIRUS-5 E1A-CONSERVED REGION-1 OR REGION-2 MUTANTS

Two conserved regions (CR1 and CR2) on the adenovirus El A proteins have previously been shown to be required for cooperation with the ras oncogene in the transformation of primary rodent cells. Sequences within these regions are essential for the ability of El A to associate with the 105K product of the retinoblastoma susceptibility gene, p105-RB, as well as with other cellular proteins, including a 107K (pl07) and a 300K (p300) species. In this paper, we show that CR1 mutants deficient in p300 binding and CR2 mutants with lost or reduced binding of p105-RB and/or p107 have a low, but not abolished focus formation activity. In contrast, CR1 /CR2 double mutants were deficient in focus formation, suggesting that the transformation activities displayed by the single CR1 or CR2 mutants were due to an independent transformation activity by both CR1 and CR2. No strict correlation between p105-RB binding and ElA-mediated transformation was observed. The El A enhancer repression function was found to correlate with the binding of p300 but not with El A-mediated transformation. Complex formation between El A and pl 07, similar to the pl 05-RB binding, required sequences within both CR1 and CR2. The CR2 sequences required for binding of p107K or p105-RB were overlapping, but not identical. Finally, a larger segment of CR2 was required for stable complex formation between ElA and phosphorylated forms of p105-RB or p107 compared to corresponding unphosphorylated species. © 1991.