EXPERIMENTAL-EVIDENCE FOR RNA TRANSSPLICING IN MAMMALIAN-CELLS

We present evidence that mammalian cells have the ability to generate functional mRNA molecules by trans-splicing. Rat cells, transformed by an early SV40 DNA fragment (BstlBam) synthesize a truncated T antigen (T1 antigen), although the cells do not have a direct sequence homology for the T1 antigen at the DNA level. The BstlBam DNA fragment encodes exclusively for the second SV40 T antigen exon (aa 83-708) and contains the entire small t antigen intron. To synthesize the corresponding mRNA (T1 mRNA), the cells utilize a cryptic 5' splice site within the second exon (codons for aa 131/132) as donor site and the upstream small t antigen 3' splice site as the acceptor site. Since these sites are in an inverted order on the pre-mRNA, two BstlBam transcripts are required to generate one TI mRNA molecule. HeLa cell nuclear extracts also performed the trans-splicing reaction in vitro.