Late messenger RNA production by viable simian virus 40 mutants with deletions in the leader region

Abstract

We have analyzed the structure of simian virus 40 messenger RNA in cells infected with mutant viruses in which DNA encoding various segments of the late leader has been deleted. The results show that large amounts of stable unspliced mRNA may accumulate in the cytoplasm and that some unspliced RNA appears in polyribosomes. The locations of the prominent 5′ ends of mRNA are influenced by relatively remote downstream sequences and bear no fixed relationship to any sequence of the simian virus 40 DNA retained in the mutant virus. Sequences downstream from the leader template may play a role in determining the region in which transcription initiates preferentially. Splices may occur even when nucleotides further than seven residues downstream from the upstream end of the splice are altered, and alternative splices with one junction in common may be differently affected by deletions near the common splice junction.