RNA processing. RNA species in cells RNA processing.

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(and some other important stuff)

From gene to protein.

Presentation transcript:

RNA processing

RNA species in cells

RNA processing

Types of introns and their removal

Types of introns

Complex organisms have intron-rich genes

Examples of introns in human protein-coding genes

Removal of introns from mRNA in the nucleus of eukaryotes

Consensus elements of human GU-AG introns

Chemistry of mRNA splicing for GU-AG introns

Three way junction at the internal (A) branch site

U1 snRNP

Spliceosome-catalyzed splicing of GU-AG introns

Different snRNPs and proteins bind and dissociate during splicing

Similarities in spliceosome-catalyzed removal of introns and self-splicing group I and group II introns

Possible errors in splice-site selection

SR proteins are essential for correct splice-site selection ESE = exonic splicing enhancers SR proteins = serine, arginine-rich proteins

Trans-splicing joins exons from different RNAs

Splicing of AU-AC introns by “minor” spliceosomes proceeds as for GU-AG introns

Alternative splicing results in alternative mRNAs that are translated into different proteins

Figure Genomes 3 (© Garland Science 2007) Alternative splicing of the human slo gene (codes for a membrane protein that regulates the flow of potassium ions across the membrane) Optional exons participating in alternative splicing events. About 500 mRNA variants are produced in cells of the inner ear.

Alternative splicing is regulated

Assembly of major and minor spliceosomes Nonsense-mediated transcript decay

Example: alternative splicing in Drosophila Dscam transcripts

Example: mutual exclusive alternative splicing of exon 6 in Drosophila Dscam transcripts

Splicing activators and repressors

Exons may code for protein domains

Exon shuffling may lead to protein diversity

Exon shuffling may be responsible for protein diversity

Figure Genomes 3 (© Garland Science 2007) Removal of introns from tRNAs

RNA processing

Processing of ribosomal RNA by cutting and trimming

Figure Genomes 3 (© Garland Science 2007) Processing of a tRNA by cutting and trimming

RNA processing

Figure Genomes 3 (© Garland Science 2007) Chemical modifications in tRNAs

Figure 12.41a Genomes 3 (© Garland Science 2007) Methylation of ribosomal RNAs

RNA editing in apolipoprotein B mRNA

Deamination of bases leads to codon changes

RNA-guided insertion of Us into mRNAs

Processing of RNAs is required for transport into the cytoplasm