lecture19 - Processing of Eucaryotic mRNAs DNA...

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Processing of Eucaryotic mRNAs DNA pre-mRNA (primary transcript) mRNA Transcription 5’ capping 3’ cleavage and polyadenylation splicing
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5’ Cap Structure on mRNAs • found on most mRNAs • rRNAs and tRNAs are not capped • protects 5’ end of mRNA from 5’ exonuclease attack • protein involved in initiation of translation binds cap • 5’ end of mRNA is modified before completely synthesized 1.
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5’ Cap Structure 7-methylguanosine linked to 5’ nucleotide by 5,5’-triphosphate linkage • 3 types of caps type 0 =methylation at N7 of added G type 1 =methylation at 2’ OH of last nt of original transcript type 2 = methylation at 2’OH of last 2 nt
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Enzymes Required for Capping         guanylyltransferase  phosphohydrolase guanine-7-methyltransferase 2’-O-methyltransferase pppNp ppNp GpppNp m7GpppNp m7GpppmNp Pi pppG PPi adoMet adohCys adoMet adohCys 5’ end of RNA transcript
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Cleavage and Polyadenylation of 3’ End • most mature mRNAs contain polyA tails (except histone mRNA) --20-250A residues added • functions to stabilize mRNA • sequence near 3’ end is polyadenylation signal = AAUAAA --recognized by cleavage and polyadenylation specificity factor (CPSF) --also find downstream U or GU-rich sequence endonuclease
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This note was uploaded on 04/06/2010 for the course BCH BCH 453 taught by Professor Heminway during the Spring '10 term at N.C. State.

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lecture19 - Processing of Eucaryotic mRNAs DNA...

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