Topic 6-L4 - Post-transcriptional regulation

Question 1

Regulation at the level of RNA

after transcription starts, but before protein is produced

Answer 1

• Transcriptional attenuation is regulation that involves prematurely
  terminating mRNA synthesis
• The stability of mRNAs can be controlled – how long before they are degraded (longer lifetime, more translation, more protein produced)
• Translation efficiency can be controlled – usually whether or not RBS is free to be bound by the ribosome (RBS structure)

Question 2

Much of this regulation at the level of RNA is executed by

Answer 2

RNA regulatory elements

Question 3

Two major RNA structures that “shut off ” gene expression

Answer 3

• transcriptional attenuation –
  premature transcriptional termination.
• Formation of a stem-loop structure involving RBS or that forms a transcriptional terminator can shut off gene expression

Question 4

During transcription, the formation of rho-independent (intrinsic) transcriptional terminators can lead to

Answer 4

transcriptional attenuation

Question 5

For translation to initiate, the ribosome binding site (RBS) of the gene
needs to be

Answer 5

“free” to bind the ribosome – not involved in base-pairing to form a “stem”

Question 6

how long an mRNA lasts (life time) affects how many

Answer 6

protein molecules will be made from that transcript

Question 7

Enzymes called ____________
degrade mRNAs and nucleotides are
recycled – all cells contain multiple
RNases

Answer 7

ribonucleases (RNases)

Question 8

All cells encode regulatory RNAs –

Answer 8

noncoding RNA whose function is to

regulate gene expression

Question 9

Bacterial sRNA (~50-300 nt long) generally exert effects by base-pairing
to target mRNA(s) to regulate

Answer 9

half-life and/or translational initiation

Question 10

Base-pairing with sRNA affects

Answer 10

RBS availability and/or RNase targeting

Question 11

One sRNA can sometimes regulate

Answer 11

many distinct target mRNAs

Question 12

An RNA chaperone called Hfq is essential for mediating the

Answer 12

regulation of half-lives

Question 13

Hfq Binds to both

Answer 13

RNAs to stabilize their interaction - in some cases also appears to recruit RNases to mediate degradation

Question 14

Riboswitches are

Answer 14

ligand-binding RNAs

• adopt intricate 3D structures that specifically bind a particular small molecule

Question 15

The binding of riboswitches allows them to

Answer 15

Sense their environment

Question 16

Riboswitches reside in the

Answer 16

5’UTR of certain bacterial mRNAs – regulate expression of downstream gene(s) on same mRNA

Question 17

Are riboswitches found in all domains?

Answer 17

Yes, but mostly in bacteria

Question 18

Riboswitches are very different from

Answer 18

sRNAs

Question 19

Ligand binding by the riboswitch changes

Answer 19

RNA structure in 5’UTR – this change induces or represses expression of downstream genes

Question 20

Ligand-binding domain called aptamer binds ligand, changes base-pairing in the 5’UTR of mRNA to affect formation of either:

Answer 20

(i) A stem-loop that sequesters the RBS (blocks translation)
ii) a transcriptional terminator that prevents transcription of the genes.

Question 21

Post-translational regulation (regulating protein levels/activity)

Answer 21

• feedback inhibition
• protein-protein interactions (bind to each other to control activity)
• post-translational modifications

Question 22

post-translational modifications –

Answer 22

enzyme adds a chemical moiety to a specific amino acid residue of a
protein, which alters its activity (change activity, or turn it “on”/“off ”)

Question 23

Like RNA, protein can also be degraded and their building blocks recycled. This is accomplished by enzymes called

Answer 23

proteases

Question 24

Proteases are essential for

Answer 24

clearing away and recycling misfolded proteins