RNA Splicing and Processing (MBG 2) PDF

unit 6 RNA : splicing and processing * different levels of gene expression regulation...

unit 6 RNA : splicing and processing * different levels of gene expression regulation - b in the nucleas in "the cytoplasm mRNA * eukaryotic vs prokaryotic guanocire ↳ eukaryotic ↳ no mRNA introns added post transcription T have · doesn't polysistronic RNA modified post transcription ↳ prokaryotic mRNA have RNA · can polysistronic A introduction ↳ RNA is important in gene expression · was characterized as an intermediate in protein synthesis · some RNAs are important for structural or functional roles > - structural ex. rRNA] gives the structure to ribosomes ↳ interrupted genes are found in all eukaryotic organisms · they are interupted by non coding sequance · most genes are uninterupted is - scerevisiae but are interupted in y multicellular eukaryotes yeast A show distribution of genes a wide sizes ↳ typical mammal has < to 8 that are spread over 16kb a gene exons short for acids · exons are usually coding - this antibiotic  regulation of the of the * expression m gene by Cstf64 ↳ Bells produce antibiotic that the cell/membrane stays in ↳ the amount of Cstf is less than the other components ↳ why· for poly advelation ? Is because it all has components a higher affinity must be for it present ↳ plasma cells produce antibiotic secreted in the blood · the amount of cstf is the same as all components but there is no limited amount · there are 1 polyadenelation Signals so alternative polyaderelation removal or excision & - intron splicing - and exon junctions b removal of introns to keep exons and linking them together of RNA Proof * splicing ↳ looping structure hear recording ↳ loops are single strand which means there is no complementry sequence maturation of * the premRNA by splicing I needs the pressence of conserved sequence at 5' and 3 end of intron ↳ intron internal sequance is needed as well Gurich region thisischpoint at any nuceta Price ↑ pyrimidine always polys peredimic as sequence endwith t ↳ intron has a conserved sequance ↳ excision splicing happens in 2 steps:] can have aternate splicing the the formation of lariat · cleavage at 5'splicing site and · cleavage at the 3'splicing site and release of laviat and ligation of neighboring exons  · first Step : > - first cleavage starts at s'intron group (oH) of the > - hydroxyl bonds to the 5' end cleared intron , it bonds at the 2-position of Ain the branch point > - formation of 5'-2' bond leads to formation of laviat > - after first cleavage the send of exonI has of free · second Step : > - second cleavage at 3' end of the intron > - 2 events happen simultaneosly of the through the 5'phosphate of 30th · bonding 2 exons exonz and of exon 1 laviat which · release of is degreded or broken down * splice some ↳ removes introns from pre mRNA ↳ made association of 150 different proteins with 5 small SnRNAs by ↳ each SuRNA links with a specific factor to mate SuRNP complexes ↳ made of 4 RNP (ribonucleic protein) complex I SnRNP I · Ul = 164 ht · vz = 188nt · U4 = 14Snt + U6 = 106nt > - they are together because they are complementry 6 · US = transcribed 116nt RNAPII all by * functions of each snRNP ↳ UI · recognize 5" splice site it is · complementry with the end of the exon and 5'splice site  ↳ u2 Complementry · to the branch point sequance except one nucleotide because it can't base pair with U2 · this is how it recognizes the "A" 304 + 06 U4 important mRNA · is in splicing · UG can participate in the catalysis of pre mRNA splicing ↳ US which is first to · Ul recognizes Us bind · it makes the exons stay togather because they are complementry * assembly of the splicesome S1 : formation of the commitment complex > - called E complex commitment of pre mRNA splicing pathway · S2 : UI complex is the first to bind Sequence 53 : U2 binds to pranchpoint S4 : UH + U6 and US bind with the UI/U2 premRNA Complex to make splice some this · requires ATP SS : 04 + 16 dissasociate and 14 leaves the complex vo but base pairs with U2 56 : US makes an extra contact with the exon of 3' 57 : after the exon is cut the intron is released with U2 , US , UG * sometimes the whole exon is considered an intron [I because they can be large and thus they can be removed ↳ alternative splicing * alternative splicing types diffrently due to 2 promoters * using 5 alternative splicing spliced de to 2 promoters having I promoters 3'alternitace splicing site due * using to presence of alternative polyaderelation * retention of an intron means it can be excluded included retention or intron * exclusion of a particular exon & removed sometimes * exons are mutually exclusive meaning only one can remain & only"one can be present * control of gene expression through alternating splicing ↳ rat troponin T gere 16-18 exons · it's a heart protein ↳ alternate exons allow adaptation to function in specific cells may alternative > have - splicing exons with alternative splicing are missing - * mRNA Stability ↳ each RNA is defined by half life ↳ regulation of protein amount avalible in cells is by the breaking down of corresponding mRNAs 3 mRNA stability involves non translated sequences of coding located in the 5 region - and 3'UTR section from · just joining a one part to the other to measure the stability ↳S and 3 sequance can have sequence elements regulating the translation · RNABP (binding protein) can interact with mRNA and regulatory proteins > - to repress/derepress translation of mRNA ↳ non fertilized vocytes have - mRNAs that are rapidly translated b fertilization after have short poly A tails ↳ · · development starts the mRNAs will be only if there first to have is fertilization cytoplasmic polyadenrelation · protein called CPEB binds to uridine rich cytoplasmic polyadenelation element > - this protein is kinase that activates when there is fertilization located in 30TRJ- untranslated transcribed region · normonal stimulation leads to CPEB phosphorelation > - this causes the protein to dissociate from CPEB and elfy z · CPEB-p starts the polyade relation bind beap to ↳ example of this is that in some organisms the has oocyte everything for embryo survival except needed one and is only translated when Sperm fertilizes it called "transationally damant * correction of mRNA ↳ it modification of mRNA by every is addition I · · suppression > - of one or more nucleotides · substitution ↳ this results information of mRNA whose sequence is diffrent from the sequance of DNA in transcription * editing by modification of a single codon ↳ example used is apolipoprotein B in humans · found in the liver > - after the editing only one nucleotide changed (Cor ( > - change happened after RNA is made so it makes shorter a sequence ↳ editing ↳ introduction of premature stop codon in mRNA leads to synthesis of a shorter protein this why one give diffrent mRNAs that are then · is gene can 2 translated to 2 different proteins > - one protein in the liver and the mother protein in the intestines