RNA degradation (lect 11) Flashcards
How are ribonucleases involved in RNA processing?
Shorten RNAs, meaning a long precursor can be converted into shorter functional RNAs
-diversifies transcripts
How was rRNA processing analysed?
Pulse-chase labelling (adding isotopic label to RNA) and viewing on gel
=> only saw rRNA, not mRNA (bc rRNA more stable)
How was heteronuclear RNA detected?
Ultracentrifugation of pulse-chase labelled RNAS
-fast-sedimentation of heteronuclear (hn) RNA seen, which is not seen in steady state samples
-most hnRNA rapidly degraded after transcription
How is transcription of non-coding RNAs suppressed?
changes in chromatin structure
eg. Set2 histone methyltransferase
How is transcription of functional RNAs quality controlled?
-turnover is default
-at every step of pathway, incorrect modifications cause the RNA to be degraded
-if processed correctly, RNA is stabilised and protected from degradation (eg. by cap, polyA, etc)
-kinetic proofreading determines whether the RNA has been processed correctly, or whether it should be degraded
Which features stabilise RNAs?
Protect them from degradation
-triphosphate (5’)
-m7G cap (5’)
-polyA tail (3’)
-histone mRNA stem loops (3’)
-assembly with ribonucleoproteins
How does kinetic proofreading work (as mode of RNA quality control)?
-GTP or ATP hydrolysis binds substrate
-if substrate correct, steps to assembly continue
-if substrate incorrect, RNA substrate is turned over
Why is kinetic proofreading carried out when it requires an energy cost?
allows efficiency
eg. in processes like ribosome assembly or spliceosome assembly
Why is RNA surveillance important?
-prevents toxic accumulation of RNA
-allows new RNAs (with new functions) to be able to evolve
What occurs when RNA surveillance systems are overburdened?
leads to disease
eg. ALS from accumulation of toxic RNA repeats in brain
