The Yersinia effector YopJ inhibits the innate immune response by blocking MAP kinase and NFkappaB signaling pathways. YopJ is a serine/threonine acetyltransferase which regulates signalling pathways by blocking phosphorylation. Specifically, YopJ has been shown to block phosphorylation of active site residues. It has also been shown that YopJ acetyltransferase is activated by eukaryotic host cell inositol hexakisphosphate. This family was previously incorrectly annotated in Pfam as being a peptidase family.