A plasmid-encoded H-NS protein selectively binds its own plasmid.

HppX CROD2, an H-NS homolog encoded by the IncX4 plasmid pCROD2 in Citrobacter rodentium, preferentially binds pCROD2 over the chromosome or other plasmids.

• Why it matters: Conjugative plasmids often encode H-NS-like proteins to help maintain plasmids and reduce fitness costs, but how specificity for plasmid DNA is achieved was unclear.
• What they did: The authors characterized HppX CROD2 binding and compared it with chromosomally encoded H-NS, including heterologous expression in Escherichia coli and testing plasmid-context effects.
• The result: HppX CROD2 shows “cognate plasmid specificity,” with much lower binding to a pCROD2 sequence when cloned in a laboratory plasmid, implying plasmid-specific DNA topology recognition.