A simplified method for large scale quantification of transcriptional activity and its use in studies of steroids and...

Chloramphenicol acetyltransferase (CAT) is widely used as a reporter to determine the transcriptional specificity of promoters and for the quantification of transcriptional activity of transcription factors such as nuclear receptors. However, large-scale quantification of CAT activity in transfected mammalian cells is still heavily labor-intensive, time-consuming and expensive. Here, we describe a simplified method that combined using multiwell tissue culture plates in transfection and sample preparation and a modified single step method for quantitatively assaying CAT activity. By using multiwell plates, the tedious sample preparation procedure was dramatically simplified. The CAT assay is performed by mixing cell lysate, chloramphenicol, 3H-acetyl co-enzyme A and non-aqueous scintillation fluid in scintillation vials, followed by automatically continuously counting samples two or three cycles at fixed time intervals. The catalytic reaction and determination of CAT activity are carried out in the vials simultaneously. This simplified protocol is faster, less expensive and more accurate than other CAT assay procedures and the results can be normalized easily. The utility of the assay is demonstrated by the analysis of the transcriptional activity of the glucocorticoid and androgen receptors cotransfected into cells with a CAT reporter.