IbrB (along with IbrA) activates immunoglobulin-binding eib genes in Escherichia coli. IbrB is related to the ParB N-terminal domain family, which includes DNA-binding proteins involved in chromosomal/plasmid segregation and transcriptional regulation, consistent with a possible mechanism for IbrB in DNA binding-related regulation of eib expression. The ParB like family is a diverse domain superfamily with structural and sequence similarity to ParB of bacterial chromosomes/plasmid parABS partitioning system and Sulfiredoxin (Srx), which is a reactivator of oxidatively inactivated 2-cys peroxiredoxins. Other families includes proteins related to StrR, a putative regulator in the biosynthetic gene cluster and a family containing a Pyrococcus furiosus nuclease and putative transcriptional regulators SbnI (Staphylococcus aureus siderophore biosynthetic gene cluster ) and EdeB (Brevibacillus brevis antimicrobial peptide edeine biosynthetic cluster). Nuclease activity has also been reported in arabidopsis Srx.