The study by Le Hir et al. (2000) reports that the spliceosome deposits multiple proteins, likely as a single complex of ~335 kDa, at a conserved position 20–24 nucleotides upstream of mRNA exon–exon junctions. This complex protects 8 nucleotides of mRNA from complete RNase digestion, and the splicing-dependent RNase protection was observed in both HeLa cell nuclear extracts and Xenopus laevis oocyte nuclei. The identified proteins in this complex include SRm160, DEK, RNPS1, Y14, and REF. The authors discuss possible functions for this complex in nucleocytoplasmic transport of spliced mRNA and the nonsense-mediated mRNA decay pathway. The findings suggest that pre-mRNA splicing can alter mRNP structure, potentially affecting downstream mRNA metabolism.The study by Le Hir et al. (2000) reports that the spliceosome deposits multiple proteins, likely as a single complex of ~335 kDa, at a conserved position 20–24 nucleotides upstream of mRNA exon–exon junctions. This complex protects 8 nucleotides of mRNA from complete RNase digestion, and the splicing-dependent RNase protection was observed in both HeLa cell nuclear extracts and Xenopus laevis oocyte nuclei. The identified proteins in this complex include SRm160, DEK, RNPS1, Y14, and REF. The authors discuss possible functions for this complex in nucleocytoplasmic transport of spliced mRNA and the nonsense-mediated mRNA decay pathway. The findings suggest that pre-mRNA splicing can alter mRNP structure, potentially affecting downstream mRNA metabolism.