What is RNA splicing?

1. What is RNA splicing? Jean Beggs Wellcome Trust Centre for Cell Biology University of Edinburgh

2. transcription messenger RNA (mRNA) translation protein Geneticinformation is transferred from genes to the proteins they encode via a “messenger” RNA intermediate DNA GENE

3. transcription intron precursor-mRNA (pre-mRNA) The intron is also present in the RNA copy of the gene and must be removed by a process call “RNA splicing” Some genes have their protein-coding information interrupted by non-coding sequences called introns. The coding sequences are then called “exons” exon 1 exon 2 intron DNA GE NE

4. transcription RNA splicing mRNA translation protein Thus expression of a gene with an intron requires an extra step to remove the intron exon 1 exon 2 intron DNA GE NE intron pre-mRNA

5. RNA is produced in the nucleus of the cell. The mRNA has to be transported to the cytoplasm to produce proteins Ribosomes are RNA-protein machines that make proteins, translating the coding information in the mRNA

6. RNA splicing mRNA AAAAAAA200 M7G transport AAAAAAA200 M7G ribosomes protein Pre-messenger RNA Processing exon exon intron pre-mRNA AAAAAAA200 M7G cap poly(A) tail nucleus cytoplasm

7. 1 2 3 5 1 2 3 5 In humans, many genes contain multiple introns intron 3 intron 1 intron 2 intron 4 4 4 Usually all introns must be removed before the mRNA can be translated to produce protein

8. 5 2 3 1 Heart muscle 5 3 1 Uterine muscle 1 3 4 5 However, multiple introns may be spliced differently in different circumstances, for example in different tissues. 2 4 Thus one gene can encode more than one protein. The proteins are similar but not identical and may have distinct properties. This is important in complex organisms

9. Step 1 intermediates Step 2 spliced mRNA Splicing a pre-mRNA involves two reactions intron branchpoint pre-mRNA A

10. pre-mRNA splicedmRNA Splicing occurs in a “spliceosome” an RNA-protein complex spliceosome (~100 proteins + 5 small RNAs)

11. We are trying to understand how spliceosomes work and how RNA splicing is regulated We are studying this in the budding yeast, Saccharomyces cerevisiae, which is a simple model organism, but the splicing machinery is very similar in yeast and humans

12. Saccharomyces cerevisiae(Baker’s yeast) • simple unicellular eukaryote • easy to study genetically • DNA sequence of entire genome known for several years • pre-mRNA splicing is highly conserved from yeast to man

13. The spliceosome is only one of many RNA-proteins machines in the cell We are studying how RNAs and proteins interact in order to understand how these machines work.

14. European Commission Acknowledgements We are grateful to the following for funding research in this laboratory: The Darwin Trust of Edinburgh