This family consists of several hypothetical Enterobacterial proteins of around 100 residues in length. Members of this family are often described as YbjC. In E. coli the ybjC gene is located downstream of nfsA (which encodes the major oxygen-insensitive nitroreductase). It is thought that nfsA and ybjC form an operon an its promoter is a class I SoxS-dependent promoter. The function of this family is unknown.