ELEMENT
WHAT IT IS
FUNCTION
CLUE · DRUG
Located in the nucleolus
Makes rRNA (28S, 18S, 5.8S)
Most abundant RNA made = rRNA
Nucleoplasm; needs general transcription factors (TFIID binds TATA)
Makes mRNA, most snRNA, miRNA
α-Amanitin → severe hepatotoxicity
Nucleoplasm
Makes tRNA, 5S rRNA
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Prokaryotic RNA polymerase
Single core enzyme (α₂ββ′ω) + σ factor
Makes all three RNA types
Rifampin (β subunit) · actinomycin D intercalates DNA (both)
Upstream site where polymerase and factors bind: TATA box (~−25) and CAAT box (~−75)
Sets where and how often transcription begins
Promoter mutation → ↓ gene expression (some β-thalassemia)
DNA site bound by activators; can be upstream, downstream or in an intron, far away
↑ transcription (DNA loops to the promoter)
Translocations put oncogenes next to Ig enhancers (Burkitt: c-MYC)
DNA site bound by repressors
↓ transcription
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Proteins with DNA-binding motifs (zinc finger, helix-turn-helix, leucine zipper)
Activate or repress genes
Steroid/thyroid hormone receptors are zinc-finger TFs
Lac operon
prokaryotic regulation
Repressor binds operator unless lactose (allolactose) present; CAP–cAMP activates when glucose is low
Genes on only with lactose present and glucose absent
Low glucose → ↑ cAMP → CAP binds → ↑ transcription
Template vs coding strand
Polymerase reads the template 3′→5′ and builds RNA 5′→3′
RNA matches the coding (sense) strand, with U for T
No primer needed — unlike DNA polymerase