Lakhotia S C, Sinha P
Chromosoma. 1983;88(4):265-76. doi: 10.1007/BF00292903.
DNA fibre autoradiography of highly polytenized nuclei in salivary glands of Drosophila nasuta larvae reveals two distinct types of active replicons. Type I replicons are longer (mean size = 64 micrometers), have a very high rate of fork migration (average rate = 0.95 micrometer/min) and generally occur in large arrays often extending over several thousand micrometers. In contrast, the type II replicons are smaller (mean size = 20 micrometers), slow replicating (average rate = 0.07 micrometer/min) and occur in short arrays containing only a few closely spaced active replicons. Evidence is presented that type I replicons are active in the early S and type II in the late S. Observations on autoradiographic labelling of partially lysed polytene chromosomes provide evidence for a lack of temporal and spatial agreement in the activation of origin points in homologous regions of the lateral polytene strands; these observations also suggest local variations in levels of polyteny within a chromosome. On the basis of this and other available information on replication in polytene chromosomes the possible roles of the two replicon types in the generation of the different 3H-thymidine labelling patterns of polytene chromosomes are discussed.
对纳氏果蝇幼虫唾液腺中高度多线化的细胞核进行DNA纤维放射自显影，揭示出两种不同类型的活性复制子。I型复制子较长（平均大小 = 64微米），具有非常高的叉迁移率（平均速率 = 0.95微米/分钟），通常以大阵列形式出现，常常延伸数千微米。相比之下，II型复制子较小（平均大小 = 20微米），复制缓慢（平均速率 = 0.07微米/分钟），并以短阵列形式出现，其中仅包含少数紧密排列的活性复制子。有证据表明，I型复制子在S期早期活跃，II型在S期晚期活跃。对部分裂解的多线染色体的放射自显影标记观察提供了证据，表明在多线侧链同源区域的起始点激活缺乏时间和空间一致性；这些观察结果还表明染色体内部多线化水平存在局部差异。基于此以及关于多线染色体复制的其他现有信息，讨论了两种复制子类型在产生多线染色体不同的3H-胸腺嘧啶标记模式中的可能作用。
