lecture11

lecture11 - RNA Processing eukaryotic mRNA cap tail...

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1101 RNA Processing eukaryotic mRNA cap tail splicing alternative splicing lower eukaryotic rRNA (Tetrahymena) prokaryotic rRNA (E.coli) prokaryotic tRNA (E.coli) eukaryotic tRNA RNA editing
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1102 The splicing reaction: eukaryotic mRNAs An intron is removed in a two-step splicing reaction 1.: 2’OH of the bp Adenine makes an nucleophilic attack to the 5’-phosphate at the 5’- intron displacing the 3’- end of the 5’-exon and forming a Lariat structure. 2.: the free 3’-OH of the liberated exon attacks the 5’-phosphate of the first base of the second exon.
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1103 Self-splicing intron of Tetrahymena rRNA --rRNAs of lower eukaryotes are processed through self splicing --it requires only free GTP (or GDP or GMP) --like pre-mRNA splicing, self splicing also occurs in two steps: 1. 3’-OH of G nucleotide attacks the 5’ phosphate of intron which results in free 3’- OH 2. Free 3’-OH attacks 5’phosphate of the 3’- intron forming a new phosphodiester bond ---after that, there is a 3rd step: Free intron undergoes cyclization reaction: 3’-OH froup attacks a phosphate 15 nt upstream of the 3’-end No function of cyclized intron is known . intron
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1104 Self-splicing intron of Tetrahymena rRNA
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1105 Only rRNA and tRNA, but not mRNA, are processed Seven operons encoding each of the three rRNAs (16S, 23S and 5S) plus several tRNAs are present in E. coli Processing occurs cotranscriptionally Several RNAses carryout processing reaction at specific sites and steps RNAsesIII, E. P, F, D, and M16, M23 and M5 are the enzymes; RNAse P is an RNA enzyme (Ribozyme) whereas the rest are protein enzymes RNA Processing Prokaryotes (E.coli)
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1106 rRNA processing in eukaryotes - Several hundred tandemly repeated copies of rRNA genes are present in the eukaryotic genome. - Transcription (by RNA pol I), processing, and ribosome assembly takes
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This note was uploaded on 10/30/2010 for the course CHEM 114C taught by Professor Alexanderhoffmann during the Spring '08 term at UCSD.

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lecture11 - RNA Processing eukaryotic mRNA cap tail...

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