ParABS system

Originally identified as a genetic element required for faithful partitioning of low-copy-number plasmids, the parABS system is a broadly conserved molecular mechanism for plasmid partitioning and chromosome segregation in bacteria. It consists of three components: the ParA ATPase, the ParB DNA-binding protein, and the cis-acting parS sequence. The parA and parB genes are typically found in the same operon, with parS elements located within or adjacent to this operon. Collectively, these components function to ensure accurate partitioning of plasmids or whole chromosomes between bacterial daughter cells prior to cell division.^[1]

Mechanism

Based on chromatin immunoprecipitation (ChIP) experiments, ParB has the ability to bind not only to high-affinity parS sites but also to adjacent nonspecific DNA, a behavior known as "spreading".^[2][3][4] The ParB-DNA complex is thought to be translocated by a Brownian ratchet mechanism involving the ParA ATPase: ParA binds DNA nonspecifically to DNA in its ATP-bound state but much more weakly in its ADP-bound state. The ParB-DNA complex binds to ATP-bound ParA, stimulating its ATPase activity and its dissociation from DNA. In this way, the ParB-DNA complex can be translocated by chasing a receding wave or depolymerizing filament of DNA-bound ParA. This translocation mechanism has been observed by fluorescence microscopy both in vivo and more recently in vitro with purified components.^[5][6][7][8]

References

1. Surtees, JA; Funnell, BE (2003). "Plasmid and chromosome traffic control: how ParA and ParB drive partition.". Current topics in developmental biology 56: 145–80. doi:10.1016/s0070-2153(03)01010-x. PMID 14584729.
2. Rodionov, O; Lobocka, M; Yarmolinsky, M (Jan 22, 1999). "Silencing of genes flanking the P1 plasmid centromere.". Science 283 (5401): 546–9. doi:10.1126/science.283.5401.546. PMID 9915704.
3. Murray, H; Ferreira, H; Errington, J (Sep 2006). "The bacterial chromosome segregation protein Spo0J spreads along DNA from parS nucleation sites.". Molecular Microbiology 61 (5): 1352–61. doi:10.1111/j.1365-2958.2006.05316.x. PMID 16925562.
4. Breier, AM; Grossman, AD (May 2007). "Whole-genome analysis of the chromosome partitioning and sporulation protein Spo0J (ParB) reveals spreading and origin-distal sites on the Bacillus subtilis chromosome.". Molecular Microbiology 64 (3): 703–18. doi:10.1111/j.1365-2958.2007.05690.x. PMID 17462018.
5. Ptacin, JL; Lee, SF; Garner, EC; Toro, E; Eckart, M; Comolli, LR; Moerner, WE; Shapiro, L (Aug 2010). "A spindle-like apparatus guides bacterial chromosome segregation.". Nature Cell Biology 12 (8): 791–8. doi:10.1038/ncb2083. PMID 20657594.
6. Ringgaard, S; van Zon, J; Howard, M; Gerdes, K (Nov 17, 2009). "Movement and equipositioning of plasmids by ParA filament disassembly.". Proceedings of the National Academy of Sciences of the United States of America 106 (46): 19369–74. doi:10.1073/pnas.0908347106. PMID 19906997. Cite uses deprecated parameter |coauthors= (help)
7. Hwang, LC; Vecchiarelli, AG; Han, YW; Mizuuchi, M; Harada, Y; Funnell, BE; Mizuuchi, K (May 2, 2013). "ParA-mediated plasmid partition driven by protein pattern self-organization.". The EMBO Journal 32 (9): 1238–49. doi:10.1038/emboj.2013.34. PMC 3642677. PMID 23443047.
8. Vecchiarelli, AG; Hwang, LC; Mizuuchi, K (Apr 9, 2013). "Cell-free study of F plasmid partition provides evidence for cargo transport by a diffusion-ratchet mechanism.". Proceedings of the National Academy of Sciences of the United States of America 110 (15): E1390–7. doi:10.1073/pnas.1302745110. PMC 3625265. PMID 23479605.