Transcriptional regulation of gene expression is controlled through the binding of sequence-specific DNA-binding proteins (transcription factors) to the regulatory regions of genes. The exact gene expression program of a cell is determined by the spectrum of transcription factors present with the nucleus of a cell. The presence of these factors is dependent upon the cell type being examined and the stimulus to which the cell has been subjected. A knowledge of the transcription factors present during any given time can be important in generating a more thorough understanding of how a cell or tissue responds to its environment. Additionally, identifying the transcription factors required for the expression of a specific gene can provide a better understanding of the molecular mechanisms involved and suggest new therapies which may specifically target an individual gene or set of genes.