Processive action of terminase during sequential packaging of bacteriophage lambda chromosomes.
Processive action of terminase during sequential packaging of bacteriophage lambda chromosomes.
复制标题
噬菌体 lambda 染色体顺序包装过程中终止酶的加工作用。
DOI：
10.1016/0022-2836(85)90395-x
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发表时间：
1985
影响因子：
5.6
通讯作者：
Miller,G
中科院分区：
文献类型：
--
作者：
Feiss,M;Sippy,J;Miller,G
噬菌体λ染色体以极化的顺序方式从多聚体DNA底物包装。当末端酶在结合染色体的粘性末端位点（cossite）引入交错切口时，就产生了成熟染色体。包装是两极化的，以染色体的起始位点和末端位点为包装可以被定义。为了启动包装，终止酶结合tocosatcosB，随后切割atcosN。为了终止染色体的包装，在末端不需要官能团B。为了解释这一发现，早先有人提出，在包装过程中，末端酶扫描的是末端标记N，而不是任何末端标记B。在这里描述的工作中，我们进行了辅助包装实验，以观察在λ染色体的顺序包装过程中是否发生了末端酶的进行性作用。辅助包装实验涉及溶酶原;串联携带三个前噬菌体的菌株。由于原噬菌体的结构类似于正常的DNA底物，因此异源免疫辅助噬菌体的感染导致被抑制的原噬菌体染色体的包装。两条染色体可以从溶原菌的前噬菌体的三个染色体之间包装出来。两个染色体包装即使centralcoisscosB-。我们对这些数据的解释是：（1）末端酶通过包装被带到中央染色体;（2）中央染色体裂解后，末端酶仍与远端染色体结合;（3）末端酶起作用，开始包装远端染色体。在我们的实验中，末端酶阅读穿过中心体以启动远端染色体包装的频率在0.3至0.5的范围内。发现阅读交叉点对cosB的状态没有很大的依赖性，表明cosB结合仅需要包装系列中的第一条染色体。一个多溶原被构建，其中初始的alcoswascos+和distalcossites是allcosB−。发现初始和下游染色体被包装。这一结果表明，包装过程中引入的末端酶不仅能够启动下游染色体的包装，而且能够扫描并终止下游染色体的包装，提出了一个以末端酶的加工作用为基础的λ染色体顺序包装模型.
Bacteriophage λ chromosomes are packaged in a polarized, sequential fashion from a multimeric DNA substrate. Mature chromosomes are generated when terminase introduces staggered nicks in the cohesive end sites (cossites) bounding a chromosome. Packaging is polarized, to the initial and terminalcossites for packaging a chromosome can be defined. To initiate packaging, terminase binds tocosatcosB, and subsequently cuts atcosN. To terminate packaging of a chromosome, a functionalcosBis not required at the terminalcos. To explain this finding, it was proposed earlier that terminase scans for the terminalcosN, rather than any subsequentcosB, during packaging.In the work described here we performed helper packaging experiments to see whether processive action of terminase occurs during sequential packaging of λ chromosomes. The helper packaging experiments involve trilysogens; strains carrying three prophages in tandem. Infection by a hetero-immune helper phage results in packaging of the repressed prophage chromosomes, since the prophage structure is analogous to the normal DNA substrate. Two chromosomes can be packaged from between the threecossites of the prophages of a trilysogen. Both chromosomes are packaged even when the centralcosiscosB−. Our interpretation of these data is that (1) terminase is brought to the centralcosby packaging; (2) following cleavage of the centralcos, the terminase remains bound to the distal chromosome; and (3) terminase acts to begin packaging of the distal chromosome. The frequency at which terminase reads across the centralcosto initiate packaging of the distal chromosome is in the range from 0.3 to 0.5 in our experiments. Reading acrosscoswas found not to be greatly dependent on the state ofcosB, indicating thatcosBbinding is only needed for packaging the first chromosome in a packaging series. A multilysogen was constructed in which the initialcoswascos+and the distalcossites were allcosB−. The initial and downstream chromosomes were found to be packaged. This result indicates that terminase that is brought to the centralcosby packaging is not only able to initiate packaging of a downstream chromosome, but can also scan and terminate packaging of the downstream chromosome.A model is presented in which processive action of terminase is the basis for sequential packaging of λ chromosomes.