Induced pluripotent stem cell (iPSC) technology is a promising approach for 
converting one type of a differentiated cell into another type of differentiated 
cell through a pluripotent state as an intermediate step. Recent studies, 
however, indicate the possibility of directly converting one cell type to 
another without going through a pluripotent state. This direct reprogramming 
approach is dependent on a combination of highly potent transcription factors 
for cell-type conversion, presumably skipping more physiological and multi-step 
differentiation processes. A trial-and-error strategy is commonly used to screen 
many candidate transcription factors to identify the correct combination of 
factors. We speculate, however, that a better understanding of the functional 
mechanisms of exemplary transcriptional activators will facilitate the 
identification of novel factor combinations capable of direct reprogramming. The 
purpose of this review is to critically examine the literature on three highly 
potent transcriptional activators: the herpes virus protein, VP16; the master 
regulator of skeletal muscle differentiation, MyoD and the "pioneer" factor for 
hepatogenesis, FoxA. We discuss the roles of their functional protein domains, 
interacting partners and chromatin remodeling mechanisms during gene activation 
to understand how these factors open the chromatin of inactive genes and reset 
the transcriptional pattern during cell type conversion.