Almost an hour after viral infection, the virus undergoes transcription to form a primary gene E1A which undergoes alternative splicing, a regulated process where multiple protein isoforms are encoded by a primary gene via exons, parts of exons or introns being differentially joined or skipped. The E1A is spliced differentially into five transcripts with sedimentation coefficients of 13S, 12S, 11S, 10S and 9S, all of which have been known to code for different proteins with varying numbers of amino acid residues of 289R, 243R, 217R, 171R, 55R, respectively, each performing different functions. The 289R and 243R proteins are the major products encoded by the E1A of Ad5. These two proteins share almost the same internal sequences as shown in the figure except for the 46 internal amino acids unique to the 289 protein which is as a result of the differential splicing. These proteins are functionally important for growth of adenoviruses.
