An exon that prevents transport of a mature mRNA | CU Experts

; In; Caenorhabditis elegans; , pre-mRNA for the essential splicing factor U2AF; 65; sometimes is spliced to produce an RNA that includes an extra 216-bp internal exon, exon 3. Inclusion of exon 3 inserts an in-frame stop codon, yet this RNA is not subject to SMG-mediated RNA surveillance. To test whether exon 3 causes RNA to remain nuclear and thereby escape decay, we inserted it into the 3′ untranslated region of a; gfp; reporter gene. Although exon 3 did not affect accumulation or processing of the mRNA, it dramatically suppressed expression of green fluorescent protein (GFP). We showed by; in situ; hybridization that exon 3-containing; gfp; RNA is retained in the nucleus. Intriguingly, exon 3 contains 10 matches to the 8-bp 3′ splice-site consensus. We hypothesized that U2AF might recognize this octamer and thereby prevent export. This idea is supported by RNA interference experiments in which reduced levels of U2AF resulted in a small burst of; gfp; expression.;

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