Transcription

Differences in promotor sequences--Different sigma factors recognize different promotor sequences and transcribe gene classes

most activators and repressors bind DNA by inserting and alpha helix into the major groove of B-form DNA

• Repression: results from competition with RNAP, the inducer binding to
• repressor prevents its binding to operator

• Activation: by cAMP/CAP in
• absence of glucose recruits RNAP by binding carboxyl-terminal domain of
• the alpha subunit

• it activated b recruiting RNA polymerase using direct potein-protein
• contacts.

• strengthens the promoter by providing another contact (how
• activation works in bacteria)

you need the O1 site to get any repression, and then the other binding sites lead to "good" repression

• Bacterial:
• -ground stat is ON
• -template is protein free
• -activators enhance weak polymerase binding
• -repressors interfere with polymerase binding
• -Promotors are DNA

• Eukaryotes:
• -ground state is OFF
• -template is chromatin (inaccessible to RNA polymerase)
• -Activators make it accessible-Repressors block activators or make chromatin less accessible
• -Promoters are PROTEIN-DNA complexes

• I- nucleolus
• II & III- nucleoplams

TATA binding protein

• 1. Chromatin remideling complexes
• 2. Histone Acetyltransferase (HAT) complexes
• 3. General Transcription Factors (TFIIB, TBP associated Factors in TFIID)
• 4. Mediator complex-associates with RNA polymerase

• acetylation
• -relieves chromatin structure
• -provides binding sites for proteins that facilitate activation

• Other types of modificatin
• methylation, phosphorylation, ubiquitination

• 1. nuclear export of mRNA
• 2. mRNA stability
• 3. mRNA translation

poly(A) polymerase

small nuclear RNAs (snRNAs) found in protein/RNA complexes called snRNPs (snurps)

Exon defined!

exon-bound SR proteins