Transcription

Regulation of transcription

Promoter: DNA sequence where RNA polymerase II and general transcription factors (e.g., TFIID) bind.
- TATA box (rich in A-T) usually located ~25 bp upstream.
- CAAT box located ~75 bp upstream.
- Mutation in the promoter results in a significant ↓ in the level of transcription.
Enhancers: DNA sequences that increase the rate of transcription by binding activator proteins.
Silencers: DNA sequences that decrease the rate of transcription by binding repressor proteins.
Note: Enhancers and silencers can be located far upstream, downstream, or even within introns of the gene they regulate. t

Initiator met-tRNA, eukaryotic IF2 (eIF2), and GTP bind to the small ribosomal subunit to form a preinitiation complex (initially a 43s preinitiation complex).
- eIF2: a small G protein
  - Binds initiator met-tRNA (ternary complex) and forms the final initiation complex by hydrolyzing GTP to GDP
  - Reconverted to the GTP-bound form by the guanine nucleotide exchange factor eIF2B
Kozak sequence: Eukaryotic consensus sequence around the start codon that enhances initiation efficiency. t

An aminoacyl-tRNA complex with eukaryotic elongation factor 1 (eEF1) hydrolyzes GTP, thereby releasing eEF1 and GDP and providing the energy for aminoacyl-tRNA to bind the A site (anticodon matches the codon of the mRNA).

A release factor recognizes the stop codon, halts translation, and hydrolytically cleaves the peptidyl tRNA bonds (requires GTP), leading to release of the protein.