Transactivation domain


The transactivation domain or trans-activating domain is a transcription factor scaffold domain which contains binding sites for other proteins such as transcription coregulators. These binding sites are frequently referred to as activation functions. TADs are named after their amino acid composition. These amino acids are either essential for the activity or simply the most abundant in the TAD. Transactivation by the Gal4 transcription factor is mediated by acidic amino acids, whereas hydrophobic residues in Gcn4 play a similar role. Hence, the TADs in Gal4 and Gcn4 are referred to as acidic or hydrophobic The activation domains, respectively.
In general we can distinguish four classes of TADs:
Alternatively, since similar amino acid compositions does not necessary mean similar activation pathways, TADs can be grouped by the process they stimulate, either initiation or elongation.

Acidic/9aaTAD

Nine-amino-acid transactivation domain defines a novel domain common to a large superfamily of eukaryotic transcription factors represented by Gal4, Oaf1, Leu3, Rtg3, Pho4, Gln3, Gcn4 in yeast and by p53, NFAT, NF-κB and VP16 in mammals. The definition mostly overlaps the older "acidic" family definition. A 9aaTAD prediction tool is available. 9aaTADs tend to have an associated 3-aa hydrophobic region immediately to its N-terminal.
9aaTAD transcription factors p53, VP16, MLL, E2A, HSF1, NF-IL6, NFAT1 and NF-κB interact directly with the general coactivators TAF9 and CBP/p300. p53 9aaTADs interact with TAF9, GCN5 and with multiple domains of CBP/p300.
The KIX domain of general coactivators Med15 interacts with 9aaTAD transcription factors Gal4, Pdr1, Oaf1, Gcn4, VP16, Pho4, Msn2, Ino2 and P201. Positions 1, 3-4, and 7 of the 9aaTAD are the main residues that interact with KIX. Interactions of Gal4, Pdr1 and Gcn4 with Taf9 have been observed. 9aaTAD is a common transactivation domain which recruits multiple general coactivators TAF9, MED15, CBP/p300 and GCN5.
Source9aaTADPeptide-KIX interaction
p53 TAD1
p53 TAD2
MLL
E2A
Rtg3E2A homolog
CREB
CREBaB6CREB-mutant binding to KIX
Gli3TAD homology to CREB/KIX
Gal4Pdr1 and Oaf1 homolog
Oaf1
Pip2Oafl homolog
Pdr1
Pdr3Pdr1 homolog

Glutamine-rich

Glutamine -rich TADs are found in POU2F1, POU2F2, and Sp1. Although such is not the case for every Q-rich TAD, Sp1 is shown to interact with TAF4, a part of the TFIID assembly.