Poxviruses replicate in cytoplasmic structures called factories and each factory begins as a single infecting particle. Sixty-years ago Cairns predicted that this might have effects on vaccinia virus (VACV) recombination because the factories would have to collide and mix their contents to permit recombination. We've since shown that factories collide irregularly and that even then the viroplasm mixes poorly. We've also observed that while intragenic recombination occurs frequently early in infection, intergenic recombination is less efficient and happens late in infection. Something inhibits factory fusion and viroplasm mixing but what is unclear. To study this, we've used optical and electron microscopy to track factory movement in co-infected cells and correlate these observations with virus development and recombinant formation. While the technical complexity of the experiments limited the number of cells that are amenable to extensive statistical analysis, these studies do show that intergenic recombination coincides with virion assembly and when VACV replication has declined to ≤10% of earlier levels. Along the boundaries between colliding factories, one sees ER membrane remnants and other cell constituents like mitochondria. These collisions don't always cause factory fusion, but when factories do fuse, they still entrain cell constituents like mitochondria and ER-wrapped microtubules. However, these materials wouldn't seem to pose much of a further barrier to DNA mixing and so it's likely that the viroplasm also presents an omnipresent impediment to DNA mixing. Late packaging reactions might help to disrupt the viroplasm, but packaging would sequester the DNA just as the replication and recombination machinery goes into decline and further reduce recombinant yields. Many factors thus appear to conspire to limit recombination between co-infecting poxviruses.

中文翻译：

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细胞质工厂，病毒装配和DNA复制动力学共同限制了痘病毒重组体的形成。

痘病毒在称为工厂的细胞质结构中复制，每个工厂都以单个感染颗粒开始。六十年前，凯恩斯（Cairns）预测这可能会对牛痘病毒（VACV）重组产生影响，因为工厂必须碰撞并混合其内容物才能进行重组。从那以后，我们证明了工厂不规则地碰撞，甚至病毒质混合不良。我们还观察到，虽然基因内重组经常在感染初期发生，但基因间重组效率较低，并且在感染后期发生。某些因素会抑制工厂融合和病毒质混合，但尚不清楚。为了对此进行研究，我们使用了光学和电子显微镜来跟踪共感染细胞中的工厂运动，并将这些观察结果与病毒的发育和重组形成相关联。尽管实验的技术复杂性限制了适合进行广泛的统计分析的细胞数量，但这些研究确实表明，基因间重组与病毒体装配同时发生，并且当VACV复制下降至早期水平的≤10％时。沿着相撞工厂之间的边界，人们看到了ER膜残留物和其他细胞成分（如线粒体）。这些碰撞并不总是会导致工厂融合，但是当工厂融合时，它们仍会夹带线粒体和ER包裹的微管等细胞成分。但是，这些材料似乎不会对DNA混合构成更多的障碍，因此病毒质也可能对DNA混合无所不在。后期包装反应可能有助于破坏病毒质，但包装会隔离DNA，就像复制和重组机制逐渐衰退并进一步降低重组产量一样。因此，许多因素似乎合谋限制了共同感染的痘病毒之间的重组。