Lecture 17 - Lecture17 scribed 1. (apoB glutamaterecepto

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Lecture 17 RNA editing is a change in the coding sequence of an mRNA after it has been tran- scribed There are two mechanisms 1. A deaminase can convert an A to an Innocine or a C to a U by oxidative deamin- ation changing the codon and hence amino acid that the mRNA specifies (apo-B, glutamate receptors) 2. In trypanosomes, many U residues are added or deleted in mitochondrial gene transcripts generating the functional mRNAs for cytochrome oxidases cox II and cox III Normally when you look at gene, it looks collinear with the mRNA that is transcribed from that DNA, the only difference would be the elimination of the introns and the trun- cation at the two different ends at the RNA specific amino acid is changed by having a single nucleotide change after transcrip- tion has occurred. one version looks like the DNA, in a different cell type there is a change in a single base that is a different base than would be expected of the DNA sequence This is called RNA editing, it always occurs after transcription and has nothing to do with differential splicing it acts specifically at the nucleotide level and not a splicing level. Due to having specific deaminase. Have to have a purine or pyrimidine that has the amino group on the base, then can oxidatively deamin- ate it using the particularly enzyme that recognizing the structure of the RNA knowing to deaminate a single base at a particular region of a particular tran- script. The transcript has to make up some sequence motif and secondary structure so that these deaminase only work on a single nucleotide. Fig 27.18 Fig 27.20 RNA editing can be directed by guide RNAs extensive RNA editing in trypanosome mitochondria occurs by insertions or dele- tions are utilized. In RNA editing there is additional U’s found in the sequence, these Us allow for frame shift mutations not to occur. RNA editing always proceeds from the 3’ end to the 5’ end. The way the cell doesn’t end up translating the partially edited RNA is by making the last U is the AUG for translation. Until the final U is added, cannot initiate trans- lation. Fig 27.21 the substrate RNA base pairs with a guide RNA on both sides of the region to be edited the guide RNA provides the template for addition (or less often, deletion) of ur- idines. The genes for cytochrome Bs ended up in little pieces, so that you have a version that lacks the uridine that is the primary transcript which is the major thing that is expressed and you have these smaller RNAs that are transcribed in separate locations called guide RNAs.
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Guide RNAs - instead of being the same sense as the primary transcript, they are complementary to the primary transcript. They are little templates that tell the edit- ing machinery how to edit. can have more than one guide RNA to do all the editing steps
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This note was uploaded on 01/26/2009 for the course BIOLOGY 244 taught by Professor Palter during the Fall '05 term at Temple.

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Lecture 17 - Lecture17 scribed 1. (apoB glutamaterecepto

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