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Ribosomal RNAs occur here with tRNAs operons
The secondary structure of the tRNAs and rRNAs is recognized by RNA’ses and used for? processing
1)Primary processing occurs during transcription by RNAse III, E, F and P (ribozyme).
2) rRNAs associate with ribosomal proteins
3)RNAse D M5, 16 and 23 carry out 5’ and 3’ mature end processing.
4) Methylation, which protects the rRNA from RNAses O2Me ribose, N6N6-dimethyl adenine.
Prokaryotic mRNA processing little to none
Where does translation occur for prokaryotes? nascent transcripts
Eukaryotic mRNA processing involves capping, splicing, polyadenylation
Capping determines the site of translation initiation
7-methylG added co-transcriptionally via 5',5'-triphosphate linkage
Cap can be differentially methylated where? 2'-OH positions of first two nucleotides
cap-0 no 2’-O-methyl, predominant in unicellular organisms
cap-1 first nt, predominant in multicellular organisms
The CAP is involved in what? Loading of ribosome onto mRNA during translation
Capping: 1: The 5' terminal triphosphate of the RNA is first removed by RNA triphosphate
Capping: 2: GTP is added by guanyltransferase
Capping:3: the 7 position of guanosine is methylated
Capping:4: mRNA is methylated by 2'-O-methyltransferase
In mammalian cells, primary transcripts have heterogeneous 3' ends
All mRNAs have poly-A tails except histone mRNA
Poly-Adenylation requires the presence of AAUAAA element
The AAUAAA element is located 10-35 nt upstream of site of poly-A tail
Poly-Adenylation also requires the presence of a U or GU rich sequence about 50 nt downstream the cleavage site
C & PA requires a dynamic assembly of multiprotein complexes: CPSF, CStF, CFI, CFII
Poly-A synthesis is catalyzed by a template independent polymerase known as PAP
Why doesn't PAP need a template? Telomere has a defined sequence
3’ Cleavage and Polyadenylation: 1: CFI and CFII cleave RNA 10-30 nuc 3' to signal
2) PolyA polymerase adds poly A tail using ATP
When does the CPSF disengage from recognition site? Tail is 10-15 nucleotides long
3) The length of the tail is controlled by PABII
Multiple copies of PABII bind to the Poly A tail to increase processivity
4) Poly(A) binding protein (PAB) binds the tails and organizes them into ribonucleoprotein particles.
Besides organizing tails/particles, what does PAB do? involved in regulating translation initiation, protect mRNA
Unlike most prokaryotic RNA transcripts, many eukaryotic transcripts contain introns
Class of intron is based on its sequence properties
mRNA splicing is coupled with transcription
mRNA splicing occurs sequentially in what direction? 5' to 3'
The transesterification reactions require no net input of energy
The transesterification reactions are catalyzed by transphosphorylation reactions
However the splicing process does require net energy input for conformational changes in the RNA and the spliceosome.
Spliceosome is a large complex (?) with more than 50 proteins 50-60S
targets include nuclear pre-mRNA transcripts that can not self splice
introns spliced by same lariat mechanism found for GII introns
Eukaryotic nuclei contain numerous copies of small RNAs (60 - 300 nt long) known as snRNA
there are five high abundant snRNAs involved in the splicing reaction: U1, U2, U4, U5, and U6
What are RNAs complementary to? Consensus sequences in the intron
Spliceosome: 1) U1 SnRNA binds the 5’ consensus sequence.
2) U2 SnRNA binds lariat sequence after the lariat is bound by the branch point binding protein (BBP)
The U2AF protein helps BBP select the intron branch point.
3) U5 SnRNAbinds to the 3' splice junction
4) A complex between U4 and U6 helps bring everything together
5)A series of rearrangements in the spliceosome generate the correct environment for different transesterification reactions.
6) Once together, U1 and U4 are destabilized and spliceosome is reactivated
Created by: ScarlettRose