Organization and expression of early genes of simian virus 40

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Abstract
The early region of SV-40 codes for at least 2 immunologically related polypeptides: large-T and small-t, with apparent MW of 90,000-100,000 and 15,000-20,000, respectively. Because small-t shares methionine-containing tryptic peptides with large-T, the 2 polypeptides are probably coded, in part, by a common nucleotide sequence. To locate the coding sequences for large-T and small-t in the DNA, the production of these proteins was examined after infection of [African green monkey kidney] CV-1 cells with wild-type and deletion mutants of SV-40. A deletion at the distal portion of the early region alters the structure of large-T but not of small-t; but deletions within the region between map coordinates 0.59 and 0.55 result in an alteration or absence of small-t and a normal large-T. These findings were rationalized by a model that proposes the existence of 2 early mRNA, 1 coding for large-T and the other for small-t. Both mRNA span virtually the entire early region; but the mRNA coding for large-T lacks the nucleotide sequence between map coordinates 0.59 and 0.54. Small-t is probably translated from the larger of the 2 mRNA, beginning at or near its 5'' end and terminating at a termination codon at about map coordinate 0.54. Large-T is translated from the shorter mRNA, beginning at the same initiator codon, and, because of the deletion of the terminator codon at 0.54, translation proceeds to the terminator codon at or near map position 0.18.

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