A phage-encoded GapR nucleoid-associated protein binds a bacterial GapR to deactivate it via an inhibitory hetero-oligomer mechanism.

RDJLα6-1 phage GapR forms heterodimers with Roseobacterial GapR that are unable to bind DNA, indicating a poison-like autoinhibitory mechanism.

• Why it matters: Phage-encoded GapR homologs infect α-proteobacteria, but how they affect the host’s essential nucleoid-associated GapR was unclear.
• What they did: Structure/function analyses and crystal structures showed RDJLα6-1 GapR is incompatible with DNA binding; localization and fluorescence assays confirmed it does not bind DNA.
• The result: Heterodimers between RDJLα6-1 and Roseobacterial GapR cannot bind DNA, supported by cellular studies, revealing a phage autoinhibitory mechanism that impacts host NAP DNA binding.