post transcriptional processing Flashcards
the primary transcript must undergo ____________ to generate a mature, translation-ready ______. A mature ______ has a 5’ and a 3’ ________________ flanking a _____________. the 5’ end has a “_____” and the 3’ end a “___________”
RNA processing; mRNA; mRNA; untranslated region (UTR); coding sequence; cap; poly-A tail
the ________ is assembled on the 5’ end of mRNA molecules by ________________.
- the 5’ cap provides __________________________
- also important for ___________________
5’ cap; capping enzyme; protection from 5’ to 3’ exonucleases; translation initiation
phosphorylation of RNA pol II CTD is necessary for:
-promoter escape (transcription initiation)
-as docking sites for RNA processing enzymes including capping enzyme, cap-binding complex, cleavage/termination complexes, RNA splicing factors
_______ continues transcription beyond the termination sequence
RNA pol II
_____________ occurs with cleavage of the endonuclease-> RNA pol II dissociates
termination
3’ end undergoes ____________ by ______________ or __________________, one of the termination factors
- a _________ is 50-100 nucleotides long
polyadenylation; polyadenylate polymerase; or poly A polymerase; poly A tail
most mRNAs in mammals undergo splicing to remove ______ sequences and link ______ sequences. The order of exons in a mRNA is identical to their organization 5’ -> 3’ in the gene.
intron; exon
the ______ governs RNA splicing. A splice junction linking the 5’ exon to the 3’ exon is formed during splicing. All the intervening intron sequence is excised.
GU/AG rule
5’ end of an intron is ____. the _______________ is immediately upstream
GU; 5’ splice site
3’ end of an intro is ____. the _______________ is immediately downstream
AG; 3’ splice site
within the intron is the __________.
branch point A
spliceosome
nuclear complex responsible for removing intron sequences and ligation of exon sequences 5’->3’ to generate a mRNA
U1 snRNP
binds to 5’ splice site in RNA
U2 snRNP
binds to the branch site and aligns it for the 1st splicing reaction
U4 snRNP
binds to and sequesters U6 snRNP
U5 snRNP
aligns the pre-RNA for the 2nd splicing reaction
U6 snRNP
promotes catalysis of splicing reactions
splicing mechanism
1. ________ is recruited to 5’ splice site
2. _______ is recruited to branch site A
3. _______ and ____________ bind to the complex to complete spliceosome assembly.
4. Dynamic rearrangement of spliceosome initiates splicing activity
- both U1snRNP and U4 snRNP exit; spliceosome is now in the catalytically active conformation
U1 snRNP; U2 snRNP; U5 snRNP; U4 snRNP/U6 snRNP
___, ___, and ______ rearrange aligning the 5’ and 3’ splice sites for the 2nd reaction
U2, U5, and U6 snRNA
small nuclear ribonuclear protein (snRNP)
complexes that make up the bulk of a spliceosome
__________ formation requires unusual __________________________
lariat; 2’-5’ phosphodiester bond
1st transesterification reaction
2’ OH of branch point A attacks 5’ P of intron
2nd transesterification reaction
3’ OH of exon attacks 5’P of downstream exon
a ___________ resulting from an error in selection of a 3’ splice site= hemophilia
splicing defect
alternative splicing
mechanism for developmental or tissue-specific production of differing mRNA (& thus proteins) from a single gene
____________ (serine/arginine rich) promote splicing by binding ______________________
SR proteins; exonic splicing enhancers (ESE)
____________________________ bind to __________________ and inhibit splicing
heterogeneous nuclear ribonuclear proteins (hnRNP); exonic splicing silencers (ESS)
RNAi
group of mechanisms in eukaryotes involving small ncRNAs that reduce expression of specific genes
___________ and ______________ act on mature mRNA in the cytoplasm.
microRNA (miRNA) and small interfering (siRNA)
miRNA
regulates both whether an mRNA can be translated and its stability
siRNA
regulates mRNA levels by direct endonuclease cleavage
- mech more important in plants
miRNA/RISC
represses translation and increases turnover of target mRNAs
- a miRNA has imperfect base pairing to the target mRNA 3’ UTR
siRNA/RISC
cleaves a target mRNA using an endonuclease activity
- siRNA cleavage requires perfect base pairing between the siRNA and the target mRNA coding sequence
______ action occurs if there is perfect base pairing between siRNA and a target mRNA
- usually a target site is located in the coding sequence of an mRNA
siRNA
________ action occurs if the base pairing is imperfect
- usually, the target site is in the 3’ UTR of an mRNA
miRNA
