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A plasmid partition system is the mechanism that assures the stable transmission of plasmids during bacterial cell division. Each plasmid has its independent replication system which control the number of copy of a plasmid in a cell. The higher the copy number is, the more likely the two daughter cells will contain the plasmid. Each molecule of plasmid diffuses randomly, so the probability of having plasmid-less cell is 21-N, where N is the number of copy. For instance, if a plasmid has 2 copies of it in a cell, there is 50% of chance of having one plasmid-less daughter cell. However, high-copy number plasmids have a cost for the hosting cell. This metabolic burden is lower for low-copy plasmids, but those have a high probability of loss after few generation. To control vertical transmission of plasmids, in addition to controlled-replication systems, bacterial plasmids use different maintenance strategies, such as multimer resolution systems, post-segregational killing systems or addiction module, and partition systems. == General properties of partition systems == Plasmid copies are paired around a centromere-like site and then separated in the two daughter cell. Partition systems involve three elements, organized in an autoregulated operon * centromere-like DNA site * Centromere binding protein (CBP) * Motor protein Centromer-like DNA site is required in ''cis'' for plasmid stability. It often contains one or more inverted repeats which are recognized by multiple CBPs. This forms a nucleoprotein complex termed partition complex. This complex recruits the motor protein, which is a nucleotide triphosphatase (NTPase). The NTPase uses energy from NTP binding and hydrolysis to directly or indirectly move and attach plasmids to specific host location (e.g. opposite bacterial cell poles). The partition systems are divided in four types, based primarily on the type of NTPases: * Type I : Walker type P-loop ATPase * Type II : Actin-like ATPase * Type III : tubulin-like GTPase * Type IV : No NTPase 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Plasmid partition system」の詳細全文を読む スポンサード リンク
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