CHROMATIN FIBER STRUCTURE - MORPHOLOGY, MOLECULAR DETERMINANTS, STRUCTURAL TRANSITIONS

Despite more than 20 years of research, the structure of the chromatin fiber and its molecular determinants remain enigmatic. Recent develop ments in high-resolution microscopic techniques, as well as the applic ation of mathematical modeling to chromatin fiber structure, have allo wed the acquisition of some new insights into the structure and its de terminants. Here we present some of the newest data on the structure o f the chromatin fiber in both its extended and compacted states, and b ring together this new knowledge with older data in an attempt to prov ide a unified view of how chromatin components interact with each othe r to form its various conformations. The structural transitions that a re believed to take place during transcriptional activation and its ce ssation are also discussed. It becomes obvious that despite some progr ess in our understanding of the fiber structure and its dynamics, huge gaps continue to exist. Bridging these gaps will require further impr ovements in already available techniques and the introduction of compl etely new approaches.