RNA SPLICING AND PROCESSING

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Export of mRNAThe EJC includes a group ofproteins called the REF family(the best characterized member iscalled Aly).The REF proteins inturn interact with a transportprotein (variously called TAP andMex) which has directresponsibility for interaction withthe nuclear poreFigure 24.17 A REF protein binds to a splicing factor andremains with the spliced RNA product. REF binds to an exportfactor that binds to the nuclear pore.B-22
Figure 24.18 Three classes of splicing reactions proceed by twotrans-esterifications. First, a free OH group attacks the exon 1–intron junction.Second, the OH created at the end of exon 1 attacks the intron–exon 2 junction.The group I and group II introns have ability to excisethemselves from an RNA. This is called autosplicing.Group I introns are more common than group II introns.In both cases the RNA can perform the splicing reaction invitro by itself, without requiring enzymatic activitiesprovided by proteins; however, proteins are almostcertainly required in vivo to assist with folding.Group II introns excise themselves from RNA by anautocatalytic splicing event.The splice junctions and mechanism of splicing of groupII introns are similar to splicing of nuclear introns.A group II intron folds into a secondary structure thatgenerates a catalytic site resembling the structure of U6-U2-nuclear intron.The 5′ exon-intron junction is attacked by a free hydroxylgroup provided by an internal 2′–OH position in nuclearand group II introns, and by a free guanine nucleotidein group I introns.B-23
Page 1 and 2: RNA SPLICING AND PROCESSINGPre-mRNA
Page 3 and 4: The physical form of hnRNA is hnRNP
Page 5 and 6: Nuclear splice junctions are short
Page 7 and 8: What ensures that the correct pairs
Page 9 and 10: The branch site in yeast ishighly c
Page 11 and 12: The five snRNPs involved in splicin
Page 13 and 14: Binding of U1 snRNP to the 5′ spl
Page 15 and 16: The direct way of forming an E comp
Page 17 and 18: Following formation of the E comple
Page 19 and 20: •Binding of U5 and U4/U6 snRNPs c
Page 21: Figure 24.16 The EJC (exon junction
Page 25 and 26: Figure 24.20 Nuclear splicing and g
Page 27 and 28: The ratio of X chromosomes toautoso
Page 29 and 30: SL RNA is a small RNA that donates
Page 31 and 32: Figure 24.26 The intron in yeast tR
Page 33 and 34: Figure 24.28 The 3’ and 5’ clea
Page 35 and 36: Figure 24.30 Splicing of tRNA requi
Page 37 and 38: 45S RNA is a precursor that contain
Page 39 and 40: RNA polymerase I terminates transcr
Page 41 and 42: •The sequence AAUAAA is a signal
Page 43 and 44: Figure 24.35 The 3 processing compl
Page 45 and 46: •Histone mRNAs are not polyadenyl
Page 47 and 48: Figure 24.38 The rrn operons in E.
Page 49 and 50: Figure 24.40 Uridine is converted t
Page 51: B-51

RNA SPLICING AND PROCESSING

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