Module 2: E. coli DNA Polymerase III and the Replisome

Question 1

Characteristics of Pol II

Answer 1

Has 3’–> 5’ exonuclease activity, no 5’–> 3’ exonuclease
May have roles in DNA repair

Question 2

What is the catalytic core made up of in Pol III

Answer 2

Alpha - polymerase subunit
Epsilon - 3’–>5’ exonuclease
Theta - weakly stimulates epsilon

Question 3

What are the three components of the Pol III holoenzyme

Answer 3

1) Two polymerase cores - one for leading and one for lagging strand synthesis
2) two beta-clamps - tether the cores to the template-primer
3) One clamp loader - consists of the gamma/tau complex (ATP required for loading)

Question 4

What components does the beta-subunit interact with

Answer 4

Alpha subunit of Pol III core and gamma/tau complex

Question 5

How does beta clamp increase processivity?

Answer 5

Allows Pol III to associate with DNA by both (alpha-template/primer) as well as (beta-alpha)
(Alpha-template/primer; alpha-beta; beta-template/primer)

Question 6

What is the minimal clamp loading machinery in E. coli?

Answer 6

Delta, delta prime, gamma, gamma, tau

Question 7

What is the function of the delta subunit of the gamma/tau complex?

Answer 7

Acts as a ‘wrench’; can interact with beta clamp and open it

Question 8

What direction does DnaB helicase track?

Answer 8

5’–>3’ on the lagging strand

Question 9

T/F: DnaG (primase) has typical palm structure

Answer 9

False: DnaG contains a toprim structure (unique to primases and topoisomerases)