In eukaryotic systems, initiation of transcription from protein-coding genes is a complex process requiring RNA polymerase II and broad families of auxiliary transcription factors. Such factors can be divided into two major functional classes: the basal factors that are required for transcription of all Pol II genes, including TFIIA, TFIIB, TFIID, TFIIE, TFIIF and TFIIH and sequence-specific factors that regulate gene expression. The basal transcription factors and Pol II form a specific multi-protein complex near the transcription start site by interacting with core promotor elements such as the TATA box, generally located 25-30 base pairs upstream of the transcription start site. ABT1 (activator of basal transcription 1) is a nuclear protein that associates with the TATA-binding protein (TBP) and enhances basal transcription activity of class II promoters. ABT1 forms a complex with ESF1, also designated ABT1-associated protein (ABTAP), which disrupts ABT1 interaction with TBP and suppresses ABT1-induced activation of Pol II-directed transcription. The ABT1/ESF1 complex colocalizes in the nucleolus and nucleoplasm.