Intervening sequences increase efficiency of RNA 3' processing and accumulation of cytoplasmic RNA

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Abstract
Two expression vectors were constructed that differ only in the presence (+) or absence (−) of an intervening sequence (IVS) in their 5'-untranslated leaders. Transient transfection into four mammalian cell lines resulted in higher levels of the Indicator protein (CAT) from the IVS(+) vector (6 to 50-old). Cytoplasmic RNA concentrations in 293s and HeLa cell lines corresponded directly to resultant protein levels; measurements In 293s cells of transcription initiation and elongation, steady-state total nuclear RNA, and cytoplasmic RNA stability, were equivalent for the two vectors. Surprisingly, the amount of poly(A)+ nuclear RNA was greater from the IVS(÷) vector. Since this difference matches the ratio seen with polyadenyiated cytoplasmic RNA, our results imply that splicing is coupled to a poiyadenylation/transport pathway.