FC0021
Promoter specific factor 1 (SP1) B domain  -  TFIID complex

Biological function
Sp1 binds a TBP associated factor TAF_II110 of the TFIID complex to activate transcription.

Structural evidence
Only structures of the zinc finger domains are available.

Biochemical evidence
A series of linker substitutions were generated in the SP1 activation domain B of 7-15 residues. Only mutations in 444-465 region affected TFIID binding and transcriptional activation. Please note that the current Uniprot sequence numbering is shifted with respect to the numbering in the paper. A glutamine-rich hydrophobic patch impacts the interaction and transcriptional activation. Replacement of bulky hydrophobic residues with alanines significantly reduces transcriptional activity. Replacements of glutamines resulted in similar activity to the wild type protein.

Structure/Mechanism
Mutations indicate that glutamine richness is not a key feature for TAF_II110 interaction. Bulky hydrophobic residues appear to be critical to mediate contacts. A common pattern alternating hydrophobic and polar (glutamine) residues may contribute to recognition.

Mechanism category
tethering

Significance
Albeit direct structural evidence is lacking, sequence independence of SP1 binding to TAF110 is an indicative of a fuzzy complex.