We have investigated the relationships among the major proteins encoded by early region 1A of Ad2 by comparative analysis of their [35S]methionine-labeled tryptic peptides using reverse phase high-performance liquid chromatography. In some instances the purified peptides were subjected to automatic sequential Edmund degradation in order to determine the position at which the methionine residues occur within the peptides. These peptides have then been located in the amino acid sequence predicted from the DNA sequence of the leftmost 4.5% of the viral genome. The data show that the 50,000, 46,000, and 42,000 molecular weight E1A proteins (all of which focus at ca. pH 6.0) obtained from Ad2-infected HeLa cells are derived from the 1.1 kb region 1A mRNA. Similarly, it is shown that two polypeptides, 58,000 (58K) and 48,000 (48K), result from cell-free translation of the 1.1 kb mRNA. The data are also consistent with the hypothesis that the in vivo 46,000, 42,000, and 38,000 molecular weight E1A proteins (all of which focus at ca pH 5.9) are derived from the 0.9 kb region 1A mRNA. Cell-free translation of this mRNA yields two polypeptides, 54,000 (54K) and 42,000 (42K).
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