CHROMATIN AND TRANSCRIPTION - HOW TRANSCRIPTION FACTORS BATTLE WITH AREPRESSIVE CHROMATIN ENVIRONMENT

The last year has seen much progress in our understanding of chromatin and transcription. Transcriptionally active chromatin has long been c orrelated with a higher level of histone acetlyation. The discovery of a nuclear histone acetyltransferase activity encoded by factors with a role in transcription raises the possibility that the cell is able t o dynamically modulate the (local) level of histone acteylation, switc hing chromatin templates from inactive to transcriptionally active sta tes. Furthermore, histone acetylation states have shown to play a role in determining the efficacy of transcriptionally silenced chromatin i n both yeast and Drosophila. The advances in our knowledge regarding t he role of the origin-recognition complex in the establishment of sile ncing, and the requirement for a locally concentrated zone of the sile nce information regulator proteins in the nucleus has provided insight s into the complex architecture of silenced chromatin. The goal of und erstanding the mechanisms by which the cell is able to 'open' repressi ve chromatin structures has prompted the discovery of multiple chromat in remodelling activites. These large protein complexes identified fro m organisms as diverse as yeast, mouse, fly and man demonstrate the ub iquity and fundamental importance of the ability to perturb the struct ure of chromatin allowing transcription of the desired genes. These da ta provide the latest and potentially most significant demonstration o f the importance of the nucleosome in the regulation of transcription.