Practice question

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.