Transcription Factor AP4 (TFAP4)

Transcription factors of the basic helix-loop-helix-zipper (bHLH-ZIP) family contain a basic domain, which is used for DNA binding, and HLH and ZIP domains, which are used for oligomerization. Transcription factor AP4 activates both viral and cellular genes by binding to the symmetrical DNA sequence CAGCTG.

The deduced 321-amino acid protein, which lacks the N terminus, contains a basic region, followed by an HLH domain, 2 leucine-rich regions, a Q/P-rich sequence, and a C-terminal acidic domain. Northern blot analysis detected a transcript of about 2 kb in HeLa cells.The leucine-rich repeats, predominantly the second repeat, mediated TFAP4 homodimerization, and the HLH domain mediated heterodimerization of TFAP4 with E12 (TCF3).