Genes have to be expressed in specific cell types at appropriate times of development dependent on external signals. cAMP signaling occurs in all cells, thus raising the question of how this signal transduction pattern is integrated into mechanisms determining cell-specific gene expression. We have analyzed expression of the tyrosine aminotransferase gene as a model to study the basis of this cell type specificity of hormone induction. We found that cell-type-specific expression is generated by combined action of cAMP signal-dependent and liver cell-specific transcription factors. The interdependence of the cAMP response element and an element determining liver cell specificity enables a gene to respond to an ubiquitous signal in a cell-specific manner
