Chloremphenicol Acetyl Transferase Gene - cat - This gene is primarily used as a reporter gene or a scoreable marker and not as a selectable marker. The gene first isolated from E. coli codes for an enzyme (CAT), which is absent in mammals and higher plants, so that whenever transferred in a gene construct, its presence can be detected by enzyme assay.

Rarely screening for this enzyme may also be used for selection of transformed regenerants, although no selection pressure can be applied.

The enzyme uses acetyl CoA + chloramphenicol (32p) as substrates and helps in the transfer of acetyl group to chloramphenicol. The presence of acetyl chloramphenicol is detected through autoradiography. The gene cat has also been used for identification of a number of regulatory sequences.