Spell R M, Holm C
Department of Cellular and Developmental Biology, Harvard University, Cambridge, Massachusetts 02138.
Mol Cell Biol. 1994 Feb;14(2):1465-76. doi: 10.1128/mcb.14.2.1465-1476.1994.
To elucidate yeast chromosome structure and behavior, we examined the breakage of entangled chromosomes in DNA topoisomerase II mutants by hybridization to chromosomal DNA resolved by pulsed-field gel electrophoresis. Our study reveals that large and small chromosomes differ in the nature and distribution of their intertwinings. Probes to large chromosomes (450 kb or larger) detect chromosome breakage, but probes to small chromosomes (380 kb or smaller) reveal no breakage products. Examination of chromosomes with one small arm and one large arm suggests that the two arms behave independently. The acrocentric chromosome XIV breaks only on the long arm, and its preferred region of breakage is approximately 200 kb from the centromere. When the centromere of chromosome XIV is relocated, the preferred region of breakage shifts accordingly. These results suggest that large chromosomes break because they have long arms and small chromosomes do not break because they have small arms. Indeed, a small metacentric chromosome can be made to break if it is rearranged to form a telocentric chromosome with one long arm or a ring with an "infinitely" long arm. These results suggest a model of chromosomal intertwining in which the length of the chromosome arm prevents intertwinings from passively resolving off the end of the arm during chromosome segregation.
为阐明酵母染色体的结构和行为，我们通过与脉冲场凝胶电泳分离的染色体DNA杂交，研究了DNA拓扑异构酶II突变体中纠缠染色体的断裂情况。我们的研究表明，大染色体和小染色体在缠绕的性质和分布上存在差异。针对大染色体（450 kb或更大）的探针可检测到染色体断裂，但针对小染色体（380 kb或更小）的探针未显示出断裂产物。对具有一个小臂和一个大臂的染色体进行检测表明，两条臂的行为相互独立。近端着丝粒染色体XIV仅在长臂上断裂，其断裂的偏好区域距离着丝粒约200 kb。当染色体XIV的着丝粒重新定位时，断裂的偏好区域也会相应移动。这些结果表明，大染色体断裂是因为它们有长臂，而小染色体不断裂是因为它们有短臂。实际上，如果将一条小的中着丝粒染色体重排形成具有一条长臂的端着丝粒染色体或具有“无限”长臂的环状染色体，它就会断裂。这些结果提示了一种染色体缠绕模型，即在染色体分离过程中，染色体臂的长度会阻止缠绕从臂的末端被动解开。
