Transcription: basal factors and activation.

Much progress has been made in the past few years in understanding the mechanism and regulation of mRNA synthesis. This rapid progress has largely been due to the availability of cloned genes encoding components of the transcription machinery. Structural and biochemical studies are rapidly defining the architecture of components in the transcription complex. Highly purified biochemical systems are beginning to elucidate the role of the individual initiation factors. The identification of a large complex that contains a polymerase, termed holoenzyme, has provided a new way of thinking about how the transcription complex assembles at a promoter. The mechanism of transcription stimulation by activators is beginning to be unraveled but still appears to be a complex process. Finally, analyses of genes involved in DNA repair, cell cycle control and transcription have revealed similarities between transcription and other forms of cell regulation.