Analysis of multiple forms of human adenovirus type 5 E1A polypeptides using an anti-peptide antiserum specific for the amino terminus.

Studies were carried out to further characterize the proteins coded for by the early 1A region (E1A) of human adenovirus type 5 (Ad5) in lytically infected cells using an antiserum prepared against a synthetic octapeptide corresponding to the amino termini of E1A products as well as another anti-peptide serum specific for the carboxy termini. Both sera precipitated the same collection of four major and two minor acidic phosphoproteins and it was confirmed that each of the 1.1- and 0.9-kb E1A mRNAs code for two major and one minor species. These data also indicated that none of the E1A species was produced by proteolytic cleavage. The deletion mutant dl313 which lacks DNA coding for the last 70 C-terminal amino acids of E1A products also produced multiple species which suggested that post-translational modifications involved in their generation do not take place in this region of the proteins. The N-terminal serum was effective in detecting neither the truncated 1.1-kb mRNA product predicted for the mutant hr1 nor the product of the small 0.6-kb E1A mRNA, suggesting that these species are either very short-lived in infected cells or exist in a conformation in which the amino terminus is inaccessable to the antibody.