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噬菌体SPP1中DNA末端切割后的连续满头部包装及其命运

Sequential headful packaging and fate of the cleaved DNA ends in bacteriophage SPP1.

作者信息

Tavares P, Lurz R, Stiege A, Rückert B, Trautner T A

机构信息

Max-Planck-Institut für Molekulare Genetik, Berlin, Germany.

出版信息

J Mol Biol. 1996 Dec 20;264(5):954-67. doi: 10.1006/jmbi.1996.0689.

Abstract

The virulent Bacillus subtilis bacteriophage SPP1 packages its DNA from a precursor concatemer by a headful mechanism. Following disruption of mature virions with chelating agents the chromosome end produced by the headful cut remains stably bound to the phage tail. Cleavage of this tail-chromosome complex with restriction endonucleases that recognize single asymmetric positions within the SPP1 genome yields several distinct classes of DNA molecules whose size reflects the packaging cycle they were generated from. A continuous decrease in the number of molecules within each class derived from successive encapsidation rounds indicates that there are several packaging series which end after each headful packaging cycle. The frequency of molecules in each packaging class follows the distribution expected for a sequential mechanism initiated unidirectionally at a defined position in the genome (pac). The heterogeneity of the DNA fragment sizes within each class reveals an imprecision in headful cleavage of approximately 2.5 kb (5.6% of the genome size). The number of encapsidation events in a packaging series (processivity) was observed to increase with time during the infection process. DNA ejection through the tail can be induced in vitro by a variety of mild denaturing conditions. The first DNA extremity to exit the virion is invariably the same that was observed to be bound to the tail, implying that the viral chromosome is ejected with a specific polarity to penetrate the host. In mature virions a short segment of this chromosome end (55 to 67 bp equivalent to 187 to 288 A) is fixed to the tail area proximal to the head (connector). Upon ejection this extremity is the first to move along the tail tube to exit from the virion through the region where the tail spike was attached.

摘要

烈性枯草芽孢杆菌噬菌体SPP1通过“满头部”机制从前体串联体中包装其DNA。用螯合剂破坏成熟病毒粒子后,由“满头部”切割产生的染色体末端仍稳定地结合在噬菌体尾部。用识别SPP1基因组内单个不对称位置的限制性内切酶切割这种尾-染色体复合物,产生了几类不同的DNA分子,其大小反映了它们所源自的包装循环。来自连续衣壳化轮次的每一类分子数量持续减少,这表明有几个包装系列在每个“满头部”包装循环后结束。每个包装类中分子的频率遵循在基因组中定义位置(pac)单向启动的顺序机制所预期的分布。每一类中DNA片段大小的异质性揭示了“满头部”切割存在约2.5 kb(基因组大小的5.6%)的不精确性。在感染过程中,观察到包装系列中的衣壳化事件数量(持续性)随时间增加。通过各种温和的变性条件可以在体外诱导DNA通过尾部排出。第一个离开病毒粒子的DNA末端总是与观察到结合在尾部的末端相同,这意味着病毒染色体以特定的极性排出以穿透宿主。在成熟病毒粒子中,该染色体末端的一小段(55至67 bp,相当于187至288 Å)固定在靠近头部(连接器)的尾部区域。排出时,这个末端首先沿着尾管移动,通过尾刺附着的区域从病毒粒子中退出。

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