Nucleotide sequence deletions within the coding region for small-t antigen of simian virus 40

Abstract

SV-40 early mutants with deletions mapping in the 0.53-0.60 region were sequenced by the Maxam and Gilbert approach. All these deletions affect the small-t gene. The size of the shortened small-t related polypeptides produced by several of the mutants was compared with the MW as deduced from the nucleotide sequence. There was good agreement for the mutants dl890, dl891 and dl2102. For dl2121 and dl2122 the small-t related protein was considerably larger than expected. It is possible to explain this result on the basis of the nucleotide sequence: the normal splicing event of the small-t mRNA still occurs, but as the deletion shifts the reading frame, translation of the small-t-related polypeptide continues beyond the small-t splice, but in a different reading frame than large-T. Mutants dl883, dl884 and dl2112 lost one of the small-t splicing boundaries, and no (or minute amounts of) small-t-related protein was observed in mutant-infected [African green monkey kidney] cells. The possible relationship between splicing and transport of poly(A)-containing mRNA from the nucleus to the cytoplasm in vertebrate cells is discussed.