[Transcription regulation--how are genes turned on and off?]

During the last 20 years much has been learned about regulation of gene activity, or transcription. Regulations are more complex in higher organisms, such as humans, than, for instance, in viruses and yeast. Therefore most of our present knowledge about gene regulation is derived from such simple systems. Recent results now suggest that a few simple mechanisms for gene activation may be shared by unrelated organisms like bacteria, yeast, flies and humans.