Amity Institute of Biotechnology, Amity University Kolkata, Kolkata 700135, India.
Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai 400076, India.
Plasmid. 2019 Mar;102:19-28. doi: 10.1016/j.plasmid.2019.01.004. Epub 2019 Feb 3.
An underlying theme in the segregation of low-copy bacterial plasmids is the assembly of a 'segrosome' by DNA-protein and protein-protein interactions, followed by energy-driven directed movement. Analogous partitioning mechanisms drive the segregation of host chromosomes as well. Eukaryotic extra-chromosomal elements, exemplified by budding yeast plasmids and episomes of certain mammalian viruses, harbor partitioning systems that promote their physical association with chromosomes. In doing so, they indirectly take advantage of the spindle force that directs chromosome movement to opposite cell poles. Molecular-genetic, biochemical and cell biological studies have revealed several unsuspected aspects of 'chromosome hitchhiking' by the yeast 2-micron plasmid, including the ability of plasmid sisters to associate symmetrically with sister chromatids. As a result, the plasmid overcomes the 'mother bias' experienced by plasmids lacking a partitioning system, and elevates itself to near chromosome status in equal segregation. Chromosome association for stable propagation, without direct energy expenditure, may also be utilized by a small minority of bacterial plasmids-at least one case has been reported. Given the near perfect accuracy of chromosome segregation, it is not surprising that elements residing in evolutionarily distant host organisms have converged upon the common strategy of gaining passage to daughter cells as passengers on chromosomes.
在低拷贝细菌质粒的分离中，一个潜在的主题是通过 DNA-蛋白质和蛋白质-蛋白质相互作用组装“segrosome”，然后是能量驱动的定向运动。类似的分区机制也驱动着宿主染色体的分离。真核细胞外染色体元件，以芽殖酵母质粒和某些哺乳动物病毒的附加体为例，拥有促进其与染色体物理结合的分区系统。这样做的同时，它们间接地利用了纺锤体力，将染色体定向移动到细胞的两极。分子遗传学、生物化学和细胞生物学的研究揭示了酵母 2 微米质粒“染色体搭便车”的几个出人意料的方面，包括质粒姐妹体与姐妹染色单体对称结合的能力。因此，该质粒克服了缺乏分区系统的质粒所经历的“母系偏向”，并在均等分离中提升到接近染色体的状态。稳定传播而无需直接能量消耗的染色体结合，也可能被少数细菌质粒利用——至少有一个案例已经报道。考虑到染色体分离的近乎完美的准确性，在进化上相距甚远的宿主生物中存在的元件都采用了相同的策略，即作为染色体上的乘客进入子细胞，这并不奇怪。
