Regulatory DNA elements of phenobarbital-responsive cytochrome P450 CYP2B genes.

This article reviews recent progress in characterizing cis-acting DNA elements of the phenobarbital-inducible CYP2B genes. Whereas proximal DNA elements such as the C/EBP binding site regulate basal transcription activity, phenobarbital-responsive enhancer activity is governed by the distal element (designated phenobarbital-responsive enhancer module, PBREM) residing about -2.3 kbp upstream from the transcription start site. Proximal elements are not required to enhance the phenobarbital-inducible transcription, since the PBREM can confer the inducibility to several heterologous promoters. Repression of the basal transcription by a negative element upstream of the -0.8 kbp region, however, may be necessary for the proper regulation of the CYP2B genes.