Overview of Eukaryotic Transcriptional Control

Question 1

How does chromatin condensation inactivate gene transcription

Answer 1

blocks RNA polymerases and general transcription factors from interacting with gene promoters

Question 2

What is the function of repressor proteins

Answer 2

• may bind to post transcription-control elements to inhibit transcription initiation via polymerase 2
• may interact with multi protein co-repressor complexes to condense chromatin

Question 3

What is the function of pioneer transcription factor

Answer 3

• binds to a specific regulatory sequence within the condensed chromatin
• interacts with chromatin-remodelling enzymes and histone acetylases that decondense the chromatin, making it accessible to RNA polymerase 2 and the general transcription factors

Question 4

What is the function of activator proteins

Answer 4

• bind to specific transcription-control elements in both promoter-proximal sites and distant enhancers
• interact with one another and with the multisubunit mediator complex to assemble general transcription factors and RNA polymerase 2 on promoters

Question 5

What initiates transcription

Answer 5

• Polymerase 2 initiates transcription
• Polymerase 2 pauses after transcribing fewer than 100 nucleotides because of action of the elongation inhibitor NELF (negative elongation factor) associated with DSIF (DRB sensitivity-inducing factor)

Question 6

What is the function of activators

Answer 6

• they promote association of the polymerase 2-NELF-DSIF complex with elongation factor P-TEFb (cyclin T-CDK9 kinase) which releases NELF
• NELF release allows resumption of RNA transcription