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#ParB

2 public questions tagged with this topic.

Microbial Physiology

The bacterial partitioning system consists of:

Bacterial genome partitioning analogous mitosis uses conserved tripartite system. Components include ParA ATPase Walker box, ParB DNA binding protein, centromere like DNA site parS. parS consists of short palindrome repeats 16 base pairs each bound specifically by ParB via helix turn helix domain, ParB CTPase forms focus spreading several kilobases forming partition complex that also loads SMC condensin MukBEF. ParA ATP dimer binds nonspecifically to nucleoid periphery, forming oscillating pattern. Interaction ParB triggers ATP hydrolysis releasing ParA allowing movement. Tripartite ParA ParB parS cassette found on chromosome near oriC for chromosome segregation in many bacteria Caulobacter, Vibrio, and on low copy plasmids P1, F for plasmid maintenance. Deletions increase plasmid loss and anucleate cells frequency drastically. System differs from divisome FtsZ FtsA cytokinesis, MinC MinD MinE division placement, MreB crescentin shape determination. Partition ensures each daughter cell inherits genetic material maintaining species continuity and antibiotic resistance plasmids dissemination stability without selection.

Ref: Livny et al., Mol Microbiol 2007, Bacterial partitioning system ParA ParB parS components.

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Microbial Physiology

What is the primary function of ParA and ParB proteins in bacterial cells?

Stable inheritance of chromosome and low copy plasmids cannot rely on random diffusion given small cell volume, requires active segregation machinery. ParA and ParB constitute conserved partition system. ParB centromere binding protein binds parS sequence palindromic heptad repeats near origin or on plasmid forming large nucleoprotein complex via spreading oligomerization stimulated by CTP binding, also recruits SMC condensin compacting DNA. ParA Walker ATPase dimeric ATP bound associates non specifically with nucleoid DNA forming gradient or filamentous cloud. ParB triggers ParA ATPase releasing ParA from DNA, creating depletion zone behind ParB parS complex, complex moves up gradient chasing higher ParA concentration toward poles via diffusion ratchet mechanism. Results plasmids chromosomes segregated to opposite halves ensuring each daughter receives genome. Function segregation of plasmids chromosomes not controlling Z-ring placement which done by Min system and nucleoid occlusion, not protein degradation nor ribosome regulation. Mutations cause high frequency anucleate cells demonstrating essentiality for viability in many species.

Ref: Baxter & Funnell, J Bacteriol, 2014, ParA ParB plasmid and chromosome segregation system.

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