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Published byAmi Walker
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RNA species in cells
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
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 12.34 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 12.40 Genomes 3 (© Garland Science 2007) Removal of introns from tRNAs
Processing of ribosomal RNA by cutting and trimming
Figure 12.17 Genomes 3 (© Garland Science 2007) Processing of a tRNA by cutting and trimming
Figure 12.18 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
Ch 17 Gene Expression I: Transcription
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Day 2! Chapter 15 Eukaryotic Gene Regulation Almost all the cells in an organism are genetically identical. Differences between cell types result from.
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