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website What is RNA splicing Jean Beggs Wellcome Trust Centre

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									     What is RNA splicing?


             Jean Beggs

Wellcome Trust Centre for Cell Biology
      University of Edinburgh
Genetic information is transferred from genes to the
    proteins they encode via a “messenger” RNA
                    intermediate

   DNA                    GENE

                               transcription

   messenger RNA
   (mRNA)
                               translation


   protein
   Some genes have their protein-coding information
interrupted by non-coding sequences called introns. The
        coding sequences are then called “exons”

                   exon 1 intron exon 2
    DNA                GE        NE

                                    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”
  Thus expression of a gene with an intron
 requires an extra step to remove the intron
             exon 1            exon 2
                      intron
DNA              GE            NE

                               transcription
                      intron
pre-mRNA

                               RNA splicing

mRNA

                               translation

protein
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
       Pre-messenger RNA Processing


                    exon   intron     exon
pre-mRNA    M7G                                  AAAAAAA200
           cap                                           poly(A) tail
                                     RNA splicing

mRNA                M7G                     AAAAAAA200

         nucleus
                                transport


        cytoplasm
                    M7G                     AAAAAAA200


       ribosomes
                           protein
 In humans, many genes contain multiple
                introns

     intron 1       intron 2       intron 3       intron 4
 1              2              3              4              5




                     1     2   3   4     5



Usually all introns must be removed before the
 mRNA can be translated to produce protein
        However, multiple introns may be spliced
       differently in different circumstances, for
              example in different tissues.
    Heart muscle         1     2       3       5




       1          2                3                 4         5




   Uterine muscle       1     3        4   5


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
Splicing a pre-mRNA involves two reactions

                       intron branchpoint

 pre-mRNA                   A



                                            Step 1


 intermediates

                                            Step 2



 spliced mRNA
      Splicing occurs in a “spliceosome”
           an RNA-protein complex




           spliceosome
     (~100 proteins + 5 small RNAs)




pre-mRNA                              spliced mRNA
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
    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
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.
                 Acknowledgements


We are grateful to the following for funding research in
                    this laboratory:




                                      The Darwin Trust
                                      of Edinburgh
European Commission

								
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