Lönn U
Chromosoma. 1981;84(2):221-9. doi: 10.1007/BF00399133.
DNA replication in Chironomus larvae that 7 days earlier passed the red-head stage is investigated. When pulse-labelled polytene chromosomes are lysed at 25 degrees C there is an enzymatic release of double-stranded DNA replication intermediates from the chromosomes. The released DNA molecules can be divided into two populations by gel electrophoresis in 1.5% agarose gels, one population is centered around slice 18 and the other population os centered around slice 27. Moreover, it is possible to chase with cold thymidine the population of labelled DNA molecules centered around slice 27 into the population centered around slice 18. The intermediates are after a time-lag joined together to produce a high molecular weight DNA which is not released from the chromosomes during cell lysis. Furthermore, in animals treated with 5-fluorodeoxyuridine the intermediates are joined together to produce a double-stranded DNA with the size expected to replicons. In contrast it is known that in late fourth instar larvae there is no subfractionation in 1.5% agarose of the DNA replication intermediates. This indicates that there is a difference in the formation of intermediates in the same tissue at two developmental stages.
对7天前已度过红头期的摇蚊幼虫的DNA复制进行了研究。当在25℃裂解脉冲标记的多线染色体时，会有双链DNA复制中间体从染色体上酶促释放出来。通过在1.5%琼脂糖凝胶中进行凝胶电泳，释放出的DNA分子可分为两类，一类集中在第18条带附近，另一类集中在第27条带附近。此外，有可能用冷胸腺嘧啶核苷将集中在第27条带附近的标记DNA分子群体追踪到集中在第18条带附近的群体中。经过一段时间的延迟后，这些中间体连接在一起形成高分子量DNA，在细胞裂解过程中不会从染色体上释放出来。此外，在用5-氟脱氧尿苷处理的动物中，中间体连接在一起形成大小符合复制子预期的双链DNA。相比之下，已知在四龄晚期幼虫中，DNA复制中间体在1.5%琼脂糖中不会出现亚分级现象。这表明在同一组织的两个发育阶段，中间体的形成存在差异。
