Unlocking the mechanisms of transcription factor YY1: are chromatin modifying enzymes the key?

The transcription factor YY1 is a complex protein that is involved in repre ssing and activating a diverse number of promoters. Numerous studies have a ttempted to understand how this one factor can act both as a repressor and an activator in such a wide set of different contexts. The fact that YY1 in teracts with a number of key regulatory proteins (e.g. TBP, TFIIB, TAFII55, Spl, and EIA) has suggested that these interactions are important for dete rmining which particular function of YY1 is displayed at a specific promote r. Two groups of proteins, previously known to function as corepressors and coactivators, that now seem likely to modulate Wi's functions, are the his tone deacetylases (HDAC) and histone acetyltransferases (HAT). These two gr oups of enzymes modify histones, and this modification is proposed to alter chromatin structure. Acetylated histones are typically localized to active chromatin while deacetylated histones colocalize with transcriptionally in active chromatin. When these enzymes are directed to a promoter through a D NA binding factor such as YY1, that promoter can be activated or repressed. This review will discuss the recent work dealing with the different protei ns that interact with YY1, with particular emphasis on ones that modify chr omatin, and how they could be involved in regulating Wi's activities. (C) 1 999 Elsevier Science B.V. All rights reserved.