RNA Maturation and Processing

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RNA Maturation and Processing Stryer 6th Chapter
29/5th 28, Lodish 6th Chapter 4.2, 8.1/ 5th 4.2,
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Gene organization, transcription, and translation
in prokaryotes
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Gene organization, transcription, and translation
in eukaryotes
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Bacterial operons produce polycistronic mRNAs
while most eukaryotic mRNAs are monocistronic and
contain introns
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Capping enzyme adds a 5 cap and creates a 5 to
5 linkage
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All mRNA precursors are polyadenylated (only
exception histones)
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Simple and complex transcription units are found
in eukaryotic genomes
alternative splicing
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Alternative splicing in different cell types
domains that bind to proteins in fibroblast
plasma membrane
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Molecular definition of a gene

• A gene is the entire nucleic acid sequence that
  is necessary for the synthesis of a functional
  polypeptide
• DNA regions that code for RNA molecules such as
  tRNA and rRNA may also be considered genes
• In eukaryotes, genes lie amidst a large expanse
  of nonfunctional, noncoding DNA and genes may
  also contain regions of noncoding DNA (introns)

rRNA gene cluster in E. coli
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Exon-intron structure in eukaryotic genomes
Exon
Yeast 6,000 genes Humans 25,000 genes
(1.5 encode for proteins, 1.5 encode for RNAs.
Rest is junk DNA (97 of our genome)
Intron
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Signal sequences for splicing
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Point mutations can affect exon-intron boundaries
in-frame STOP codon in intron
Mutation creates new 5 splice site
message is spliced incorrectly (STOP codon
becomes part of coding sequence)
low hemoglobin-beta production resulting in anemia
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RNA splicing
In ciliate rRNA
In humans
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Spliceosome mediated intron removal
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Catalysis is driven by small nuclear RNAs, not
primarily by proteins
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• What you need to know
• Pre m-RNA is processed by
• adding a cap to the 5 end (only known 5 to 5
  link in nucleic acid)
• the cap is important for translation initiation
• 2) polyadenylation, which is thought to
  increase mRNA half-life
• splicing (group I, II self-splicing, or
  spliceosome-assisted.
• Spliceosome composed of snRNPs, which
  contain snRNAs)
• snRNAs drive the reaction, not the proteins.
  Different steps can be
• carried out in the test tube and do not require
  protein to be present.
• alternative splicing provides tissue-specific
  protein variants
• Introns are encoded in the DNA. In the mRNA
  transcript, they can be
• recognized as 5splice site, branch point and
  3splice site. The intron
• begins with GU and ends with AG. The branch
  point is usually an A.