Promoter activity in transfected eukaryotic cells is generally studied by linking the promoter sequence to a gene that encodes an easily detectable “reporter” protein, such as chloramphenicol acetyltransferase (CAT), β-galactosidase (β-Gal), or luciferase (Luc).
The bacterial enzyme chloramphenicol acetyltransferase (CAT, type I), encoded by Tn9 and having no eukaryotic equivalent, has become one of the standard markers used in transfection experiments. Traditionally, CAT activity is measured using a radioisotopic CAT assay.
