W10L2 regulation of translation in prokaryote

Question 1

importance of Translational regulation of ribosomal proteins

Answer 1

-Ribosomal RNA and ribosomal protein must be stoichiometrically co-regulated

Question 2

Translational regulation of ribosomal proteins In e.coli

Answer 2

-Ribosomal protein genes are arranged in operon
-gene dosage experiments reveal autorepression of ribosomal protein operon
-insertion of spc operon into e.coli, double the gene dosage, mRNA but only one ribosomal protein

Question 3

How are rRNA and ribosomal proteins autorepressed?

Answer 3

• Ribosomal proteins 1 and 2 interact with rRNA to assist formation of 2nd structure
  -Ribosomal protein 1 and 2 are on the same operon
  -If rRNA is in excess, all protein will bind to rRNA
  -If ribosomal protein are in excess, protein 2 bind to mRA prevent translation of protein 1
  -protein 1 orf then pair with protein 2 ORF
  -translation of ORF2 is inhibited by structure in mRNA

Question 4

Translational regulation of the spc operon by ribosomal S8 protein

Answer 4

-The S8 protein acts as a translational repressor of the L5 ORF by binding to 16s rRnA
-If in excess, ribosomal protein S8 binds to the translation initiation region in the mRNA (contain AUG) encoding S8, thus inhibiting translation of itself.
-S8 have a higher affinity for 16S>mRNA
Translation of spc operon, S8 protein binds to 16S rRNA
Excess of S8 protein:
binds to RBS in spc mRNA, prevents translation

Question 5

How Trans-acting small RNAs (sRNAs) can regulate translation initiation positively or negatively

Answer 5

sRNA binds to mRNA:
a. Inhibiting formation of secondary structure, allowing ribosomes to initiate at RBS/AUG
b. Preventing translation initiation at RBS/AUG

Question 6

Osmolarity response - involves a sRNA

Answer 6

• consist of a two component system

-DNA binding domain regulates porin gene expression
-Porins : OmpF and OmpC protein form pores in the membrane
-size of the pore influences solute flow into cell, osmolarity

Question 7

Osmolarity in depth

Answer 7

-two components system active
-lead to increase expression of OmpC, also activate micF
-micF - binds to ompFmRNA inhibiting translation
translation
-Phosphorylation of OmpR activates OmpC and inhibits ompF expression

Question 8

Riboswitches can regulate transcription termination

Answer 8

• when the riboswitch is bound at the aptima, it can change the secondary structure of the mRNA, cannot bind by ribosome

Question 9

E. coli lysC riboswitch regulates translation initiation

Answer 9

lysC riboswitch is in mRNA upstream of a Lys transporter ORF and a Lys biosynthesis ORF
-the present of lysine change the Aptima so it cannot be translated
-in the ON position, RNase E site are hidden but exposed in the OFF position

Question 10

E. coli lysC riboswitch regulates type

Answer 10

• non-nucleolytic repression mechanism (no degradation )
  -Nucleolytic repression mechanism (yes degradation)

Question 11

An RNA thermosensor regulates translation in Listeria

Answer 11

-PrfA is a virulence protein required for host infection at 37ºC
-but transcript is present at both 20’ and 37’
-due to changing structure of the hairpin loop (secondary structure) at high temperature allow ribosome to bind
-GC rich need more energy to denature
-mutation of nucleotide required for secondary structure mRNA structure abolishes thermosensing

Question 12

Regulation of translation termination by RF2

Answer 12

Abundant RF2:
Ribosomes terminate RF2mRNA translation at codon 26
Limiting RF2:
Ribosomes do not terminate RF2mRNA translation
-Ribosomes shift reading frame to translate full ORF
RF2 regulates its own expression by translation termination
-If translation is NOT terminated (by RF2) the ribosome shifts frame due to an internal RBS sequence