Homologous SV40 RNA trans-splicing: Special case or prime example of viral RNA trans-splicing?

To date the Simian Virus 40 (SV40) is the only proven example of a virus that recruits the mechanism of RNA trans-splicing to diversify its sequences and gene products. Thereby, two identical viral transcripts are efficiently joined by homologous trans-splicing triggering the formation of a highly transforming 100 kDa super T antigen. Sequences of other viruses including HIV-1 and the human adenovirus type 5 were reported to be involved in heterologous trans-splicing towards cellular or viral sequences but the meaning of these events remains unclear.

Homologous SV40 RNA trans-splicing: a new mechanism for diversification of viral sequences and phenotypes.

Simian Virus 40 (SV40) is a polyomavirus found in both monkeys and humans, which causes cancer in some animal models. In humans, SV40 has been reported to be associated with cancers but causality has not been proven yet. The transforming activity of SV40 is mainly due to its 94-kD large T antigen, which binds to the retinoblastoma (pRb) and p53 tumor suppressor proteins, and thereby perturbs their functions.

SV40 T1-mRNA trans-splicing and translation requires that the in vitro synthesized cRNA is capped before microinjection.

The purpose of this investigation was to study the effect on cap structure for trans-splicing in mammalian cells. The early SV40 Bst/Bam pre-mRNA (cRNA) was synthesized in vitro in both capped (cap-Bst/Bam-cRNA) and non-capped (Bst/Bam-cRNA) versions and microinjected into the nuclei of TC7 cells. Trans-splicing was monitored by immunofluorescence staining (T1-antigen) and by RT-PCR analysis.

In vitro synthesized SV40 cRNA is trans-spliced after microinjection into the nuclei of mammalian cells.

We present for the first time experimental evidence that in vitro synthesized RNA (cRNA) is trans-spliced after microinjection into the nuclei of mammalian tissue culture cells. The template used for cRNA synthesis was the early SV40 BstXl/BamHI DNA fragment. This DNA fragment encodes exclusively for the second T-antigen exon and contains the intact small t-antigen intron.