Pii: S0962-8924(99)01679-7

Dept of Structural Biology, Stanford School of Medicine, Stanford, CA 94305, USA. M any molecules involved in eukaryotic transcription and its control have now been identified, including nucleosomes, polymerases, general transcription factors and the regulatory apparatus. Recent excitement in the field stems, in part, from two findings. First, transcriptional coactivators and corepressors function by enzymatic modification of histones to modulate repression by nucleosomes. Second, Mediator, first defined in yeast, is an important basis of regulation by nuclear receptors and other transcription control proteins in mammalian cells. Additional key insights into the transcription mechanism have come from studies of prokaryotic RNA polymerases.