Identification of the phosphorylation sites in early region 1A proteins of adenovirus type 5 by amino acid sequencing of peptide fragments.

We have mapped the positions of three of the phosphorylation sites on the 289 and 243 residue (289R and 243R) early region 1A (E1A) proteins of human adenovirus type 5 (Ad5). These proteins, which play roles in both transcriptional control and oncogenic transformation, have identical sequences except for the presence in 289R of 46 additional internal amino acids. Phosphorylation was detected exclusively at serine residues. E1A proteins purified …