Wright Lecture 8: Catabolite Repression and Transcription Termination

Question 1

cAMP

Answer 1

Intracellular concentration of cAMp in bacterial cells is carefully maintained by rates of enzymatic synthesis and degradation
Glucose inhibits the activity of adenylate cyclase, which decreases the intracellular concentration of cAMP in bacterial cell

Question 2

Adenylate cyclase

Answer 2

Enzyme that synthesizes cAMP from ATP

Question 3

Catabolite activator protein (CAP)

Answer 3

Required for maximal initiation of lactose operon and other operons that code for enzymes required for sugar metabolism
CAP binds to CAP site in promoter: entry site for RNA polymerase is destabilized allowing RNA polymerase binding
CAP must be bound and repressor off for operon to be turned on

Question 4

Rho-independent termination

Answer 4

1. Inverted repeat followed by string of approximately 6 adenine nucleotides
2. Inverted repeats are transcribed into RNA
3. Inverted repeats in RNA fold into hairpin loop which causes RNA polymerase to pause: destabilizes DNA-RNA pairing (GC rich stem)
4. The hydrogen bonds in the A-U base pairs break
5. RNA transcript separates from the template, terminating transcription
   * *RNA termination from a hairpin loop followed by a string of uracils

Question 5

Rho-dependent termination

Answer 5

1. Rho binds to unstructured region of RNA and moves towards 3’ end, following RNA polymerase
2. RNA polymerase pauses when it encounters terminator sequence and Rho catches up
3. Using helices activity, rho unwinds RNA-RNA hybrid and brings transcription to an end
   Stem in rho-dependent termination (vs. rho-independent) is not GC rich or have run of uracils
   Depending on abundance of rho, different mRNAs are produced generating different polypeptides by a single operon

Question 6

Differences between Rho-independent and Rho-dependent termination step

Answer 6

Rho-dependent has GC rich stem and run of uracils on RNA

Rho-independent has neither

Question 7

Mutations in rho-independent sequence

Answer 7

Results in rho-dependent termination at this site

Mutations in hair pin and deletion of uracil string