Edelman J R, Lin Y J
Department of Science, Borough of Manhattan Community College, City University of New York, New York 10007, USA.
Cytobios. 2001;106(413):171-91.
The phenomenon of sister chromatid exchange has remained an enigma in that the actual mechanism for its formation has never been elucidated. It has long been suspected that the process involves some form of breakage and rejoining of DNA, but that hypothesis has never been proved. Recent work in this laboratory using cells from a premature aging disorder (Werner's syndrome) has promulgated the hypothesis that heterochromatin may not be an integral structure of chromosomes, but rather serves as a surface feature or covering. Furthermore, heterochromatin in Werner's syndrome chromosomes was found to be unstable and easily sloughed-off the chromosome surface. In this investigation evidence is presented which shows that incorporation of bromodeoxyuridine into DNA causes instability in the purported heterochromatin covering, resulting in translocation of segments of heterochromatin from the unifilarly-substituted chromatid to the bifilarly-substituted sister chromatid. Such translocation may represent the long-elusive mechanism of sister chromatid exchange formation.
姐妹染色单体交换现象一直是个谜，因为其形成的实际机制从未得到阐明。长期以来人们一直怀疑这个过程涉及某种形式的DNA断裂和重新连接，但这一假设从未得到证实。本实验室最近使用来自一种早衰症（沃纳综合征）的细胞进行的研究提出了这样一个假设，即异染色质可能不是染色体的一个整体结构，而是作为一种表面特征或覆盖物。此外，发现沃纳综合征染色体中的异染色质不稳定，很容易从染色体表面脱落。在这项研究中，提供的证据表明，将溴脱氧尿苷掺入DNA会导致所谓的异染色质覆盖物不稳定，从而导致异染色质片段从未经双取代的染色单体转移到经双取代的姐妹染色单体上。这种转移可能代表了长期以来难以捉摸的姐妹染色单体交换形成机制。
