Toxin domain, YhfG. Protein of unknown function (DUF2559). This family of proteins appear to be restricted to Enterobacteriaceae. The sequences are annotated as yhfG however currently no function is known.

Crystal structure of an HEPN domain protein (TM0613) from Thermotoga maritima at 1.75 A resolution. [PDB ID: 1o3u] [PudMed:14997578]
Structure of HI0074 from Heamophilus Influenzae reveals the fold of a substrate binding domain of a nucleotidyltransferase [PDB ID: 1jog] [PudMed:12486719]