《分子生物学》第13章 RNA剪接（英文教学课件）非AI生成 (2).ppt

Alleukaryoteshaveintrons,andyettheseelementsarerareinbacteria.Twolikelyexplanationsforthesesituation:1.Intronsearlymodel–intronsexistedinallorganismsbuthavebeenlostfrombacteria.2.Intronslatemodel–intronsneverexistedinbacteriabutratheraroselaterinevolution.5-1Exonsareshuffledbyrecombinationtoproducegeneencodingnewproteins*Whyhavetheintronsbeenretainedineukaryotes,andinparticular,intheextensiveformseeninmulticellulareukaryotes?*1.Theneedtoremoveintrons,allowsforalternativesplicingwhichcangeneratemultipleproteinsfromasinglegene.2.Havingthecodingsequenceofgenesdividedintoseveralexonsallowsnewgenestobecreatedbyreshufflingexon.*5-2Threeobservationssuggestexonshufflingactuallyoccur:1.Thebordersbetweenexonsandintronswithinageneoftencoincidewiththeboundariesbetweendomainswithintheproteinencodedbythatgene.某特定基因的外显子和内含子的交界处经常与该基因编码蛋白质的结构域的边界相一致。*Forexample:DNA-bindingproteinFigure13-26*2.Manygenes,andproteinstheyencode,haveapparentlyarisenduringevolutioninpartviaexonduplicationanddivergence.许多基因及其所编码的蛋白质明显是进化过程中部分地通过外显子复制和变异而产生。*3.Relatedexonsaresometimesfoundinunrelatedgenes.ExonshavebeenreusedingenesencodingdifferentproteinsFigure13-27*Topic6

RNAEDITING*6-1RNAeditingisanotherwayofchangingthesequenceofanmRNAI.Sitespecificdeamination1.AspecificallytargetedCresiduewithinmRNAisconvertedintoUbythedeaminase.2.Theprocessoccursonlyincertaintissuesorcelltypesandinaregulatedmanner.Figure13-30*ThehumanapolipoproteingeneStopcodeInliverInintestinesStopcodeFigure13-29*ExamplesofRNAeditinginmammals*IIGuideRNA(引导RNA)-directeduridineinsertionordeletion.1.ThisformofRNAeditingisfoundinthemitochondriaoftrypanosomes(锥虫).2.MultipleUsareinsertedintospecificregionofmRNAsaftertranscr