Lec23 - Lecture 23 Eukaryotic RNA Processing 2 Processing...

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Lecture 23 Eukaryotic RNA Processing 2 Processing of mRNA (continued) Differential pre-mRNA processing Trans-splicing RNA editing Processing of tRNA Processing of rRNA Alternative splicing Alternative 3’ end processing (Lodish 6th Ed. Chapter 8) (Lodish 5th edition Chapter 12)
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Differential pre-mRNA processing Differential pre-mRNA processing can produce different mRNAs and cognate proteins from a single gene: Eukaryotic Proteome >> Genome About 35-60% of human genes are “complex” (minimal estimate based solely on alternatively spliced genes). Complex transcripts / mRNAs are generated by: 1. Alternative splicing of pre-mRNAs (3. Alternative promoter usage --> not a mRNA processing event ! ) “Simple” genes “Complex” genes one gene one transcript / mRNA one protein one gene Several different transcripts / mRNAs (complex transcripts) Several different proteins (isoforms) with several different functions
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Optional exon (exon skipping) Mutually exclusive exons Alternative 5’ splice sites Alternative 3’ splice sites 5’ 3’ Optional intron (intron skipping) Alternative splicing Constitutive alternative splicing: alternatively spliced transcripts for a given gene are generated at a fixed ratio in most conditions and cell types. Regulated alternative splicing: when specific spliced products of a given gene are favored over others in specific tissues, at specific developmental stages or in response to specific physiological stimuli. Requires specific RNA-binding proteins “splicing regulators” that determine which intron/exon junctions are favored by the splicing machinery (spliceosome). mRNA1 mRNA2 1 2 3 3 3 2 1 1
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Positive regulation: Negative regulation: splicing activator Splicing NO splicing x repressor NO splicing x Splicing Pre-mRNA mRNA Pre-mRNA mRNA Tissue 1 Tissue 2 Induced cell state Uninduced cell state Splicing activators are RNA-binding proteins that stimulate spliceosome assembly. Splicing repressors are
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Lec23 - Lecture 23 Eukaryotic RNA Processing 2 Processing...

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