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Lecture 29 - Trans-splicing - BIOL308.pdf

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BIOL 308
Bruce Wolff

Lecture 29Processing control TranssplicingFound mostly in protozoa and C elegansmRNAs are constructed by splicing or separate RNA moleculessplicesome joins exon of one gene with the exon of another geneSome messages are polycistronic units this type of splicing enables creation of monocistronic mRNAfrom polycistronic primary transcriptsSplicing of the mini exonswith coding exonstriggers polyadenylation of the 3 end In trypansomaMany 140 nt leader sequencesEach transcribed and spliced39 nt leader mini exonMini exons will splice with 5 end exons of all protein coding transcripts contained in polycistronic primary transcript They lack internal intronsProcessing control Inhibited polyadenylationEg U1 A ProteinOne of several proteins from the UsnRNP complex U1AU1A proteincan bind to two identical sites upstream of the poly A signal in its own premRNA autoregulation PIEBinding will inhibit only polyadenylation and not cleavagemRNA for the U1A protein is degradedOccurs when excess U1A presentCoordinates expression of U1A with U1 snRNP assembly Transport through Nuclear PoresNuclear envelope is perforated by pores that can selectively transport macromolecules across the membrane both directionOnly functional mRNAsare exported5 capis recognized by transport machinery Its necessary for transportIn nucleus the premRNAs do not exist as free molecules associated with proteins hnRNPsSome proteins associated with processed mRNANuclear mRNPs messenger RNPs are exported together with mRNA into cytoplasmAs mRNAnuclear mRNPs pass through nuclear pore nuclear mRNPs get replaced with cytoplasmic mRNPsNuclear proteins shuttle back NOTES FROM LECTURES Page 1
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