ABSTRACT
Animal tissues are made up of cells with distinctive properties that result from selective gene expression. Each cell type expresses a specific set of protein products and has a characteristic pattern of growth and cell cycle regulation. To mediate this selective gene expression, each cell type expresses a distinctive mixture of transcription factors. The mixture consists of general ‘housekeeping’ transcription factors, which are common to most cells, and specialized ‘tissue-enriched’ transcription factors. Multiple factors bind to each gene and combine their activities, efficiently integrating multiple signals into a single transcription unit (Carey, 1998). Genes that define a cell phenotype, e.g., serum albumin in the liver, are regulated by a combination of housekeeping and tissue-enriched factors. The latter generate the phenotype of the cell, but are not sufficient to activate transcription without the housekeeping factors.
