RNAs in Gene expression Flashcards
How is X-chromosome inactivation an example of RNA mediated gene expression?
In females, random X inactivation occurs to allow for dosage compensation.
This occurs by an RNA transcript Xist binding along the length of the silenced chromosomes.
Xist is transcribed from the X-inactivation centre, is polyadenylated and spliced but retains in the nucleus and is not translated.
What is the function of Tsix and PcG proteins in X-inactivation
Tsix is antisense transcript of Xist. Regulates expression of Xist.
PcG proteins are corepressor complexes (eg enhancer of Zeste) These are HMTs, promote chromatin condensation
Describe and example of RNA mediated repression in yeast
During growth in Glucose, gal gene is inactive
however, H3K9me (epigenetic marker of transcription) is found downstream of Gal10.
Gal10 is expressed at low levels and binds Gal gene ensuring its repression
What is the difference between CUTS and SUTS?
CUTS = cryptic unstable transcripts found in yeast - degrade quickly
SUTS are stable unannotated transcripts
What is the purpose of toggling at promoters?
Promoters are usually bidirectional, expression from the reverse direction of functional expression might produces CUTS. This allows a quick response to transcription factors.
Discuss the transcription interference mechanism at Ser3 in yeast
Ser3 is a gene required for serine biosynthesis, highly repressed in normal conditions.
Non coding RNA is generated from region upstream of Ser3 gene = SRG1
SRG1 blocks binding of TFs at Ser3 promoter
How can RNAinterference (RNAi) cause mrNA degradation?
dsRNA from variety of sources (viral, endogenous etc) can be cut by Dicer enzymes
Makes staggered end cuts, releases shorts dsRNA fragments
Rapidly separates to ssRNA molecules.
This ssRNA can incorporate into mRNA or genes by base pairing causing mRNA degradation (RISCS) or transcriptional repression (RITS)
