ABSTRACT
Eukaryotic gene promoters are divided into different functional regions: the core promoter, adjoining the start point of transcription to the 5'-end, and the proximal/distal promoter, located further upstream. In both pro- and eukaryotes, gene transcription is regulated according to the same principle: transcription-controlling proteins rather than genomic DNA are the targets of input signals. Two general pathways exist for signal transduction from the cell's periphery into the nucleus: signals that are unable to penetrate the cell membrane are intercepted by transmembrane receptors and give rise to the formation of second messengers or activate other secondary reactions. Phosphorylation of the polymerase is catalyzed by several protein kinases, which are under the control of exogenous signals. As co-activators and co-repressors are substrates of protein kinases and other protein-modifying enzymes, highly sophisticated cross talk occurs between different signaling pathways. The work of the histone-modifying enzymes is further supported by translocases that interrupt the histone–DNA bonds by mechanical force.
