Equipositioning of chromosomes in the polyploid archaeon Haloferax volcanii by HpaAB.

HpaA and HpaB on secondary chromosome pHV3 in Haloferax volcanii enable equipositioning of pHV3, with HpaA localization altered by residue mutations and HpaB acting as a centromere-binding factor.

• Why it matters: Genome segregation in archaea is poorly understood, and high ploidy in Haloferax volcanii has been assumed to yield random partitioning despite distinct chromosome organization.
• What they did: The study characterized HpaA (a ParA-like ATPase) and HpaB (a ParB-like centromere-binding protein) on pHV3, using residue mutations, gene deletions, localization assays, and single-particle tracking.
• The result: Deleting hpaA and hpaB caused severe growth defects on xylose as the sole carbon source, reduced the pHV3-to-main chromosome ratio, and single-particle tracking indicated HpaB influences HpaA dynamics.

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