13 - Review: Transcription of protein coding genes: Review:...

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Review: Transcription of protein coding genes: Review: Transcription of protein coding genes: mRNA-like strand
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Review: 1. Initiation 2. Elongation 3. Termination Transcription of protein coding genes: Review: Maturation of mRNA : Pre-mRNA 5’ capping 3’ Polyadenylation Splicing Mature mRNA
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Pre-mRNA Processing • mRNA processing takes place in nucleus • Translation in cytoplasm Processing of Eukaryotic Pre-mRNA 1. 5’ cap 2. 3’ Poly(A) 3. Splicing Introns Exons 4. Co-transcriptional processing
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5’ Cap addition to pre-mRNAs Special 5’-5’ linkage Form of guanine with a methyl group at 7’ position +1 nucleotide Functions of 5 cap • marks as mRNA • protection • export signal • translation Additional methyl groups at 2’ position - extent depends on organism Pre-mRNAs are always associated with nuclear proteins: hnRNAs - heterogeneous nuclear RNA •Collective term including pre-mRNA and other nuclear RNA of various sizes hnRNPs - heterogeneous nuclear ribonucleoprotein particles (RNA + protein) •Prevent mRNA secondary structure- facilitates subsequent processing steps •Contribute to processing (ex. splicing) by associating with specific sites on mRNA and interacting with proteins involved in processing event •Involved in mRNA export from the nucleus
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3’ cleavage and polyadenylation Sequences in the pre-mRNA direct this process 5’ m 7 G AAUAAA 3’ G/U Poly(A) site Poly(A) signals AAUAAA - signal to cleave and add A’s G/U - rich region 3’ to the AAUAAA signal G/U rich region 3’ cleavage and polyadenylation: 1. protein factors bind poly(A) signals (cleavage/polyadenylation complex) 2. cleavage at poly(A) site 3. poly(A) polymerase (PAP) must bind prior to mRNA cleavage - no exposed end adds A’s to create a poly(A) tail
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Slow - addition of first 12 A residues by poly(A) polymerase (PAP) Rapid - addition of ~250 A residues •also by PAP •rapid addition occurs only after PABPII binding PAP PABPII 5’ m 7 G AAUAAA 3’
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This note was uploaded on 03/31/2010 for the course BIMM bimm 100 taught by Professor Dr.sato during the Winter '08 term at UCSD.

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13 - Review: Transcription of protein coding genes: Review:...

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