Prokaryotic transcription/translation regulation

Question 1

Expressome

Answer 1

RNA polymerase and the ribosome

Question 2

Polycistronic transcription

Answer 2

ORF preceded by ribosome binding site (RBS) or Shine-Dalgarno

Ribosome can associate at any ORFs so one mRNA can produce multiple proteins

Question 3

Ribosome sites

Answer 3

A site holds aminoacyl tRNA
P site holds tRNA with growing polypeptide attached
E site holds tRNA before exit

Question 4

Prokaryotic ribosomes

Answer 4

70s made up of 50s (large) and 30s (small) subunits

Composed of rRNA including 16s and proteins

Question 5

Ribosome binding site

Answer 5

Shine Dalgarno sequence

6-8 nucleotides upstream of initiating AUG

Complementary to 3’ end of 16s rRNA

Question 6

Attenuation

Answer 6

Termination of transcription

trpL leader sequence precedes terminator. Followed by structural genes

if trp is high, attenuator forms terminator loop.

If trp is low, attenuator forms antiterminator loop

Question 7

TRP operon control

Answer 7

Repressor binding at operator stops initiation or attenuation prevents elongation

Question 8

Translation regulation by regulator proteins

Answer 8

Bind to mRNA at AUG or RBS to block translation

Gene 32 of phage T4 self-regulates. Excess gp32 binds to RBS in own mRNA and prevents translation

Question 9

Translation regulation by mRNA structure changes

Answer 9

Bacteriophage cistron translation requires changes in mRNA secondary structure.

Translation of preceding cistron may open up RNA and expose second AUG (initiation) site

Question 10

Translation regulation by operon binding

Answer 10

r-proteins control own translation

Associate with rRNA when available and mRNA translation continues

When rRNA is absent, r-proteins accumulate and bind to mRNA to prevent translation. Occurs in adverse growth conditions

Question 11

sRNA

Answer 11

small non-coding RNA
Can form duplex in RNA to prevent regulatory protein binding

Binding to mRNA may create a site for attack by endonucleases

Binding to mRNA may prevent formation of secondary structure

Question 12

Bacterial regulator RNAs

Answer 12

17 different sRNAs
Hydrogen peroxide activates transcription activator OxyR

Activates oxyS gene which encodes a small RNA regulator

OxyS RNA binds RBS and initiation site of fhIA TF mRNA

Question 13

Riboswitch

Answer 13

RNA domain that contains a sequence to change its secondary structure and control its activity

Question 14

Alteration of mRNA stability

Answer 14

RyhB non-protein coding mRNA can deregulate the stability of mRNA and predispose it to degradation by RNAse III

Question 15

Drugs targeting the ribosome

Answer 15

Aminoglycosides inhibit translocation of the ribosome

Macrolides and Ketolides bind within exit tunnel of ribosome