Control of Transcription in Eukaryotes

Question 1

Eukaryotes’ 3 nuclear RNA polymerase

Answer 1

• RNA-P I - synthesises rRNA
• RNA-P II - Synthesises mRNA
• RNA-P III - Synthesises small cellular RNAs (tRNA, 5s rRNA)

~100 protein factors are needed w/ RNA-P II to drive transcription at all promoters

Question 2

RNA polymerase II Transcription Factors - GTFs

Answer 2

• General Transcription Factors (GTF-2H for example is as big as RNA-P)

Question 3

RNA polymerase II Transcription Factors - Regulatory Factors

Answer 3

Activators - require multiple for most genes
Co-activators - helper proteins that act as a ‘velcro’ forming a molecular bridge between activator + RNA-P/GTFs
- Covalently modify / remodel chromatin to facilitate transcription

Question 4

Repressors + Co-repressors

Answer 4

Black transcription
- However chromatin does this
- Target + activate a gene

Question 5

Eukaryotic Promoters - Core

Answer 5

Overlaps transcription start site + binds GTFs and RNA-P II
- may include TATA box - analogous to bacterial -10 sequence

Question 6

Enhancers + Proximal Promoter Elements

Answer 6

Regions of DNA that bind activator proteins
- can be distant from transcription

Question 7

Transcription via Recruitment

Answer 7

Activators bind enhancers + proximal promoter sequences
- Recruitment GTFs and/or RNA-P II recruit a co-activator (mediator) which recruits GTFS + RNA-P II

Question 8

Transcription - ground state:off

Answer 8

• Transcription occurs in a chromatin context which s a general repressor of gene transcription
  -jnjnne

Question 9

Epigenetic Modifications - DNA methylation

Answer 9

Linked to transcription repression

Question 10

Epigenetic Modification - Histone Acetylation

Answer 10

• Linked to transcription activation

Question 11

Epigenetic modification - Histone Methylation

Question 12

X-inactivation - Epigenetic process

Answer 12

• In female mammals where 1 X chromosome is inactivated in each cell
• Due to DNA methylation (inactive X along whole thing) which leads to histone deacetylation + condensed chromatin
• Occurs in embryo leading to mosaicism (one or other X made inactivated)
• Condensed chromosome can be seen in somatic cells

Question 13

Transcription of yeast GAL1 gene

Answer 13

• In absence of galactose, Gal80 protein represses Gal4 activation