Serine/threonine-protein acetyltransferase translocated into infected cells, which mediates acetylation of serine and threonine residues of host target proteins. acetyl-CoA + L-threonyl-[protein] = CoA + O-acetyl-L-threonyl-[protein] acetyl-CoA + L-seryl-[protein] = CoA + O-acetyl-L-seryl-[protein] Belongs to the acetyltransferase YopJ family.