transcription basics

Question 1

Ciprofloxacin

Answer 1

Quinolone antibiotic
Binds to the A subunit of bacterial DNA gyrase.
DNA cleavage and resealing activity impaired.
No sealing of double-strand breaks: DNA damage

topoisomerase inhibitor

Question 2

Novobiocin

Answer 2

Coumarin antibiotic
inhibits bacterial DNA gyrase by binding to the ATP binding site in its B subunit.
Inhibits its DNA anti-supercoiling activity.
Transcription of many bacterial genes disrupted

topoisomerase inhibitor

Question 3

Rifampin

Answer 3

(rifampicin) –
A broad-spectrum antibiotic used for mycobacterial infections, in immunosuppressed patients, and tuberculosis.
Drug blocks the initiation of transcription by binding to a protein pocket near the active site of the β subunit of the BACTERIAL polymerase to block the path of the nascent RNA during initiation.

Point mutation(s) in bacterial beta subunit changes rifampin binding site.
No binding of rifampin
Resistant bacteria in the population take over.
Drug becomes ineffective- resistance develops.

Question 4

Actinomycin D

Answer 4

Oligopeptide tails clamp the drug to the minor groove of DNA.
Phenoxazone ring gets intercalated between two GC pairs.
How does this drug affect transcription?
It blocks movement of RNA polymerase.

blocks both prokaryotic and eukaryotic transcription because binds to the DNA

Question 5

mushroom poisoning

Answer 5

Amanita phalloides, a mushroom, synthesizes α-Amanitin.
α-Amanitin is a cyclic octapeptide.
Binds to and inactivates the largest subunit of RNA polymerase II, RPB1. (only in eukaryotes)
Consequences of Amanita phalloides consumption: latency of 6-24 hours
Cell death in gastrointestinal mucosa, liver, and kidneys
Vomiting, bloody diarrhea, abdominal cramps, leading up to liver and kidney failure.