005 RNA Splicing (Processamento).pdf

7/29/2019 005 RNA Splicing (Processamento).pdf

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04. RNA splicing


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75% dos genes humanos sofrem splicing


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Modelo geral de splicing

DNA

hnRNA

mRNA

Nucleo

Citoplasma

53

5

3 5


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Tipos de processamento (splicing)

-Nuclear(eucariotas)Sequencias consenso intro/exo (GT.....AG)

snRNPs (small nuclear Ribonuclear Particles) U1.....U6

-Self splicingMitocondria em algumas bacterias

Grupo I -> Guanosina como factor (thermophila)

Grupo II -> sequencia especfica (GT....AG) Intro/Exo

(I e II possuem estruturas secundrias muito complexas)

(RNA funciona como uma emzima Ribozyma)

-Enzimaticaligase de splicing (S.cerevisiae, Xenopus)


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O splisossoma utiliza os RNAs dos snRNPs para orientar

a reao


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Fungos filamentosos

Mitocondria


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Exon skipping or cassette exon: in this case, anexon may be spliced out of the primary transcript

or retained. This is the most common mode inmammalian pre-mRNAs.

Mutually exclusive exons: One of two exons isretained in mRNAs after splicing, but not both.

Alternative donor site: An alternative 5' splice

junction (donor site) is used, changing the 3'

boundary of the upstream exon.Alternative acceptor site: An alternative 3' splice

junction (acceptor site) is used, changing the 5'

boundary of the downstream exon.

Intron retention: A sequence may be spliced out asan intron or simply retained. This is distinguished

from exon skipping because the retained sequence

is not flanked by introns. If the retained intron is in

the coding region, the intron must encode aminoacids in frame with the neighboring exons, or a

stop codon or a shift in the reading frame will

cause the protein to be non-functional. This is the

rarest mode in mammals.


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Splicing Alternativo


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Splicing occurs as transcription takes place


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Alternative splicing: how to get more proteins out ofyour genome

30,000 human genes probably give more than 100,000 different proteins

21 3 4 calcitonin 5 CGRP 6

5 3

21 3 4 calcitonin

21 3 4 calcitonin 5 CGRP 6

21 3 4 calcitonin

21 3 5 CGRP 6

AAAA

AAAA

DNA

NuclearTranscripts

mRNAs

ProteinsThyroid

Neurons


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Down Syndrome Cell Adhesion Molecule

Axon guidance in the CNS


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Alternative splicing of the -tropomyosin gene from rat. -tropomyosin is a coiled-coil proteinthat regulates contraction in muscle cells. The primary transcript can be spliced in different

ways, as indicated in the figure, to produce distinct mRNAs, which then give rise to variant

proteins. Some of the splicing patterns are specific for certain types of cells. For example, the

-tropomyosin made in striated muscle is different from that made from the same gene in

smooth muscle. The arrowheads in the top part of the figure demark the sites where cleavageand poly-A addition can occur.


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Escolha do local de processamento


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Splicing Alternativo (fast and slow Pol II)


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RNA editing

EucariotasVirus

tRNAs

rRNAs

mRNAs

miRNAs

No RNA editing in prokaryotes

mRNA - Can alter AA sequence, splice site

RNA degradation change from Adenosine to Ionosine leads to RNA degration

RNA structure different protein binding site


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RNA editing


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Editing in trypanosomes


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Mechanism of A-to-I RNA editing in mammals. The position of an edit issignaled by RNA sequences carried on the same RNA molecule. Typically, a

sequence complementary to the position of the edit is present in an intron,and the resulting double-stranded RNA attracts the A-to-I editing enzyme

ADAR. Mice and humans have three ADAR enzymes: ADR1 is required in theliver for proper red blood cell development, ADR2 is required for proper

brain development and the role of ADR3 is not yet known.

Adenine:Inosine

adenosine deaminases acting on RNA (Purine Biosynthesis)

Inosine:citosine


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Apolipoprotein B

005 RNA Splicing (Processamento).pdf

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