A small RNA complementary to an intervening sequence is produced late in SV40 infection

Abstract

The post-transcriptional modifications that affect simian virus 40 (SV40) mRNA are similar to those undergone by most eukaryotic mRNAs and include 5′-end capping, 3′ polyadenylation and splicing of mRNA precursors¹. Late in SV40 infection unspliced 19S RNAs are found predominantly in the nucleus whereas the spliced 19S RNAs are mainly cytoplasmic^2,3. Nuclear and cytoplasmic 19S RNAs differ in that all the cytoplasmic species have lost a 32-nucleotide intervening sequence located between 0.760 and 0.765 map units^3,4. Previous transcriptional studies of SV40 deletion mutants implied that splicing of the late nuclear transcripts and transport of RNA into the cytoplasm were coupled events⁵. More recent studies, however, demonstrate that transport of unspliced 19S RNA can occur when the sequences encompassing the 32-nucleotide intervening sequence (0.760–0.765 map units) are deleted⁶. We have previously proposed that this small 19S RNA intervening sequence may be involved in the retention of the unspliced RNA within the nucleus³. One hypothesis to account for recognition of the 32-nucleotide intervening sequence by a nuclear retention system postulates the existence of a small nuclear RNA complementary to the intervening sequence. We describe here the initial characterization of a small nuclear RNA made late in SV40 infection which is complementary to the DNA of the 19S intervening sequence. Several host cytoplasmic RNAs also hybridize to this intervening sequence.