Lecture 27 - Post-Transcriptional Regulation Flashcards
What are Balbiani rings?
Balbiani rings are sites of particularly active RNA synthesis on polytene chromosmes. They form large puffs on the chromosome and result in mRNPs that are large rings.
What did Michael Taylor from UofT publish in Nature in late october? How did he determine this?
He published works showing how U1 snRNAs are often mutated in certain types of cancer. He analyzed brain tumours extracted from patients (via various methods, like NGS) to determine whether certain markers are present or particular mutations occur, among other things.
Where and by what is mRNA secondary structure broken apart in nuclear export?
Secondary structure is broken apart by the RNA helicase on the cytoplasmic side of the membrane.
What interacts with the 3’ poly-A tail when it passes through the NPC?
Cytoplasmic Proteins
What occurs during the pioneering roung of translation?
The ribosomes move along a mRNA that has passed through the NPC and kick off any proteins on the mRNA which were not removed by the RNA helicase. They drop off the mRNA when they get to the termination codon around the poly-A tail.
What happens to remaining nuclear proteins after the pioneering round of translation?
They make their way back to the nucleus.
What are in-frame stops?
In-frame stops are mutations that give rise to truncated proteins that the cell recognizes as either damaging or toxic due to them having a dominant-negative effect.
What is a dominant-negative protein?
A dominant-negative protein is a protein that interferes with cellular processes. In many cases, this variant protein will be worse than eliminating the original protein altogether.
How can a receptor binding to a ligand on the outside of a cell enact changes within the cell?
It can change transduce that signal to alter the transcriptional output.
What might happen if a receptor protein is truncated?
It might interact with ligands but fail to transduce the downstream effect. The receptor might sequester all the ligands from functional receptors. You end up getting a loss of function caused by the truncated receptor being unable to transduce the genetic repertoire that it normally should when bound to a ligand.
When and how are truncated proteins recognized by the cell?
The truncated proteins are often recognized by the cell in the pioneer round. When the ribosome makes its way through the mRNA and meets a premature stop site, it will “hang out” for a while to assess the problem. The proteins associated with exons in the downstream mRNA will curl up and interact with the stalled ribosome, serving as a signal for nonsense-mediated mRNA decay (NMD).
What happens when NMD is triggered?
If the nonsense-mediated mRNA decay response is triggered, the associated mRNA will be deadenylated and destroyed very rapidly, preventing potential damage caused by a truncated protein.
What is the level of mRNA a function of?
It is a function of the synthesis rates and rates of degradation.
What is the half-life of E. coli mRNA? What is the half-life of human mRNA?
3-5 Minutes
10 Hours
What do organismal variations in mRNA half-life reflect?
These half-lives reflect the way in which organisms live in their environments. Organisms that must change very rapidly in response to nutritional cues have short mRNA half-lives while organisms with stable environments have long half-lives.
