Lecture 8 - Oxidative regulation of Pol III transcription

Question 1

Describe features of Pol III

Answer 1

Transcribes short RNAs

Has only 3 promoter types

It can facilitate reinitiation

It is regulated by the growth signalling pathway or tumour suppression

Does not require ATP hydrolysis or elongation factors

Question 2

Describe Brf2 binding

Answer 2

EMSA showed Brf2 does not bind to DNA on its own

Single-molecule FRET showed the complect stability increased as follows:
TBP, TBP+Brf2, TBP+Brf2+BDP1

Question 3

Describe aspects of Brf2 structure

Answer 3

R110 participates in sequence binding affinity

Y260 participates in sequence recognition

The Arch interacts with the upstream factor SNAPc

SNAPc helps recruit Brf2

The TBP anchor domain is responsible for interaction of TBP/Brf2 on and off DNA

Question 4

Describe Oxidation in the complex

Answer 4

The molecular pin contains a cysteine residue that can be oxidised

Oxidation of C361 can regulate complex binding, impairing DNA binding

Question 5

Describe the Mechanism of control of Brf2 in healthy cells

Answer 5

Under oxidative conditions, Pol III transcription is evaded

Transcript of SeCys tRNA is not formed, which is required to counteract the effects of oxidative stress

Under prolonged oxidative stress, SeCys tRNA becomes a limiting factor, leading to apoptosis in healthy cells

Question 6

What happens in cancer cells?

Answer 6

Brf2 is overexpressed, so SeCys tRNA continues to be expressed, leading to further proliferation

Question 7

Summarise the role of Brf2

Answer 7

Brf2 acts as a redox sensor, placing Pol III under redox control

Brf2 controls the level of ROS that cells can cope with before triggering apoptosis