This review focuses on the roles of cis- and trans-acting factors that …

• Abstract
• Introduction
• POL II CTD and coupling
• Cross-talk proteins
• Alternative splicing reveals strong links between transcription an splicing
• The roles of transcriptional activators in alternative splicing
• POL II elongation
• Slow polymerases and alternative splicing
• Pauses to POL II elongation affect splicing
• From transfected minigenes to endogenous genes
• Reciprocal coupling: how splicing affects transcription
• Concluding remarks
• Acknowledgements
• References
• Figures
• Tables

Biology Articles » Molecular Biology » Multiple links between transcription and splicing » Slow polymerases and alternative splicing

Slow polymerases and alternative splicing

- Multiple links between transcription and splicing

Slow polymerases and alternative splicing

A more direct proof for the elongation mechanism in the transcriptional control of alternative splicing in human cells was provided by the use of a mutant form of pol II (called C4) with a lower elongation rate (Chen et al. 1996). Human cells were transfected with reporter minigenes for alternative splicing together with vectors expressing an -amanitin-resistant human pol II large subunit carrying the C4 mutation. After treatment with -amanitin, the endogenous pol II becomes inhibited and the reporter minigenes are transcribed by the recombinant, elongation-defective mutant. The slow polymerase was shown to stimulate the inclusion of fibronectin EDI exon by threefold, confirming the hypothesis of inverse correlation between elongation rate and inclusion of this alternative exon. The C4 mutation also affected the splicing of Adenovirus E1a, by favoring the use of the most upstream of the three alternative 5'-splice sites that compete for a common 3'-splice site. The explanation for this effect is that a reduction in elongation rate would allow more time to assemble splicing complexes at the upstream 5'-splice site. However, inclusions of other alternative exons such as exon 7B of the heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1-E7B) gene were not affected by the slow polymerase (de la Mata et al. 2003).

Similar effects of pol II elongation rates on splicing were found in yeast. Alternative splicing is a very rare event in yeast. By mutating the branchpoint upstream of the con stitutive internal exon of the DYN2 gene, Howe et al. (2003) created an artificial cassette exon that becomes alternatively spliced. Skipping of this exon can be partially prevented when expressed in a yeast mutant carrying a slow pol II or in the presence of elongation inhibitors. This supports the hypothesis that what is important to the balance between exon skipping and exon inclusion is the relative rates of spliceosome formation and pol II processivity (Fig. 4).