Mondal Neelima, Parvin Jeffrey D
Department of Pathology, Brigham and Women's Hospital and Harvard Medical School, MA 02115, USA.
Crit Rev Eukaryot Gene Expr. 2003;13(1):1-8. doi: 10.1615/critreveukaryotgeneexpr.v13.i1.10.
Although nature's design of the DNA double helix is ingenious for the storage of information, this design creates topological problems for the processes that occur on the DNA. Cellular processes, such as transcription, replication, chromosomal segregation, and chromosomal condensation, are all complicated by the double helix. The problem is compounded in cells since the DNA is in chromatin. Topoisomerases relax positive and negative superhelical turns in DNA, and thereby topoisomerases have long been recognized as key components of the DNA replication and chromosome segregation and condensation machinery. A role for topoisomerases in the transcription process has also been noted in living cells, but only recently has such a role been recapitulated in the test tube for transcription reactions. New data are discussed that demonstrate that for in vitro transcription reactions, topoisomerases are dispensable when the template is naked DNA, but when the template is reconstituted into chromatin, topoisomerases are required for transcription to proceed efficiently.
尽管大自然设计的DNA双螺旋结构对于信息存储而言十分巧妙，但这种设计给发生在DNA上的过程带来了拓扑学问题。细胞过程，如转录、复制、染色体分离和染色体浓缩，都会因双螺旋结构而变得复杂。由于DNA存在于染色质中，细胞中的问题更加复杂。拓扑异构酶可松弛DNA中的正超螺旋和负超螺旋，因此长期以来，拓扑异构酶一直被认为是DNA复制、染色体分离和浓缩机制的关键组成部分。在活细胞中也已注意到拓扑异构酶在转录过程中的作用，但直到最近才在试管中重现了这种作用于转录反应的角色。本文讨论了新的数据，这些数据表明，对于体外转录反应，当模板为裸露的DNA时，拓扑异构酶是可有可无的，但当模板重组为染色质时，转录过程高效进行则需要拓扑异构酶。
