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

Chloramphenicol acetyltransferase (CAT) is widely used as a reporter to det ermine the transcriptional specificity of promoters and for the quantificat ion of transcriptional activity of transcription factors such as nuclear re ceptors. However, large-scale quantification of CAT activity in transfected mammalian cells is still heavily labor-intensive, time-consuming and expen sive. Here, we describe a simplified method that combined using multiwell t issue culture plates in transfection and sample preparation and a modified single step method for quantitatively assaying CAT activity. By using multi well plates, the tedious sample preparation procedure was dramatically simp lified. The CAT assay is performed by mixing cell lysate, chloramphenicol, H-3-acetyl coenzyme 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 o f 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 ass ay is demonstrated by the analysis of the transcriptional activity of the g lucocorticoid and androgen receptors cotransfected into cells with a CAT re porter.