Positive Cofactor 4 (PC4)

The latter include TBP-associated factors (TAFs), which interact with the activation domains of various regulatory proteins to enhance transcription. A second group of positive cofactors includes PC1, PC2, and PC3; they are distinct from TFIID and are present in the so-called upstream stimulatory activity (USA) cell fraction. These factors also have a strong positive influence on transcription. A third group of factors isolated from the USA fraction suppress transcription.

The 127-amino acid protein was demonstrated to be a single-stranded DNA-binding protein and the recombinant PC4 was shown to function identically to the native protein through its interaction with TAFs. Protein kinase CK2, in conjunction with the coactivator PC4, established DPE-specific transcription.