Acetyltransferase (or transacetylase) is a type of transferase enzyme which transfers an acetyl group.include:Histone acetyltransferases including CBP histone acetyltransferase ; Choline acetyltransferase ; Chloramphenicol acetyltransferase; Serotonin N-acetyl transferase .Chloramphenicol acetyltransferase (or CAT) is a bacterial enzyme that detoxifies the antibiotic chloramphenicol and is responsible for chloramphenicol resistance in bacteria.

This enzyme covalently attaches an acetyl group from acetyl-CoA to chloramphenicol, which prevents chloramphenicol from binding to ribosomes.CAT is used as a reporter system to measure the level of a promoter or its tissue-specific expression. The CAT assay involves monitoring acetylation of radioactive chloramphenicol on a TCA plate because acetylation significantly changes migration rate.