BCH311H1 Lecture Notes - Cleavage And Polyadenylation Specificity Factor, Consensus Sequence, Polyadenylation
22 Jul 2014
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Document Summary
Splicing (eukaryotes) lec#2: splicing occurs post-transcriptionally in eukaryotes but not in prokaryotes. Other rna besides mrna, rrna and trna are components of nuceloproteins with a variety of functions e. g. splice introns and process rrna + trna. Primary transcript 5"-end is enzymatically capped with m7g via a 5" 5" cap to stabilise mrna against endonucleases degradation and phosphatise degradation of the 1st phosphate. Eukaryotes only have 3 caps (0,1,2): i. ii. iii. iv. P of gtp attacks -p of atp using guanylyl transferase to release ppi (g) + pi (a) = gmp + adp. Gmp with a ribose sugar upside down forms the 1st cap i. e. cap 0 to allow 5" 5" link formation. Cap 0 n7 is methylated using s-adenosyl methionine to form m7g. Subsequent methylations of ribonucleotides downstream occur using the same enzyme i. e. 2"-oh of ribose is methylated. 3"-polyadenylylation of mrna produces a consensus sequence aauaaa aka poly(a) addition site in order for transcription termination to occur.
