The prediction of transcription factor binding sites in genomic sequences is in principle very useful to identify upstream regulatory factors. However, when applying this concept to genomes of multi- cellular organisms such as mammals, one has to deal with a large number of false positive predic- tions since many transcription factor genes are only expressed in specific tissues or cell types. We developed TS-REX, a database/software system that supports the analysis of tissue and cell type- specific transcription factor-gene networks based on expressed sequence tag abundance of transcrip- tion factor-encoding genes in UniGene EST libraries. The use of expression levels of transcription factor- encoding genes according to hierarchical anatomi- cal classifications covering different tissues and cell.
