Serine/threonine-protein acetyltransferase translocated into infected cells, which mediates acetylation of serine and threonine residues of host target proteins (By similarity). Induces a hypersensitive response (HR) in tomato cv. Hawaii 7998 (S.lycopersicum) carrying the resistance gene (PubMed:10430949, PubMed:8274773). acetyl-CoA + L-threonyl-[protein] = CoA + O-acetyl-L-threonyl-[protein] acetyl-CoA + L-seryl-[protein] = CoA + O-acetyl-L-seryl-[protein] Probably secreted via a type III secretion system (TTSS). No longer inhibits growth of bacteria encoding this gene on tomato cv. Hawaii 7998. Belongs to the acetyltransferase YopJ family.