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#plasmid segregation

2 public questions tagged with this topic.

Microbial Physiology

The ParM-ParR-ParC system in bacteria is responsible for:

Type II partition system ParM ParR ParC extensively studied molecularly via electron microscopy and total internal reflection fluorescence revealing filaments pushing plasmids. parC centromere comprises two clusters five 11 base pair direct repeats separated binding ParR dimers forming helical clamp around DNA. ParR directly interacts with ParM filament ends increasing elongation rate. Filaments grow bipolarly inserting monomers at parC ParR junction producing pushing force separating plasmids by up to cell length. After plasmids reach poles ParM hydrolyzes ATP destabilizing filaments recycling monomers. While some literature loosely describes adaptor interactions with membrane, primary function not membrane anchoring but segregation ensuring each daughter inherits plasmid. System analogous to eukaryotic anaphase B spindle elongation. Mutations in ParM Walker A lysine abolish ATPase eliminate plasmid stability increasing loss rate thousand fold. Understanding ParM ParR ParC mechanism informs synthetic biology construction stable low copy vectors and insight how bacteria solve problem genome distribution without nuclear envelope and mitotic apparatus using cytoskeletal polymers.

Ref: Moller-Jensen et al., EMBO J 2002, ParM-ParR-ParC segregation pushing plasmids - Type II system.

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Microbial Physiology

Which protein plays a role in bacterial plasmid segregation?

Low copy plasmids require faithful segregation to avoid loss during division that would be frequent if distribution random. Actin like protein ParM encoded by many IncE plasmids R1 provides pushing mechanism. ParM ATPase polymerizes into left handed double helical filaments structurally resembling F actin despite low sequence identity, two protofilaments wound. Filaments exhibit dynamic instability both ends grow ATP bound, hydrolysis induces catastrophe. In plasmid context, centromere site parC contains repeat sequences bound by adaptor ParR which forms helical oligomer encircling parC forming ring. ParR ring caps plus ends ParM filaments stabilizing them promoting elongation that pushes two plasmid ParR parC complexes apart towards opposite cell poles prior septation. Thus ParM plays role bacterial plasmid segregation via actin like spindle. FtsZ tubulin homolog cell division, MreB maintains rod shape via elongasome, MamK positions magnetosome chain chain. Discovery ParM demonstrated bacteria possess true cytoskeleton capable force generation similar eukaryotic mitosis but simplified, target for understanding plasmid stability biotechnology maintaining industrial plasmids without antibiotic selection pressure.

Ref: Garner et al., Science 2007, ParM role in bacterial plasmid segregation - actin homolog.

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