The pCAT®3 Reporter Vectors provide a basis for the quantitative analysis of factors that potentially regulate mammalian gene expression. These factors may be cis-acting, such as promoters and enhancers, or trans-acting, such as various DNA-binding factors. The backbone of the pCAT®3 Reporter Vectors is similar to the pGL3 Luciferase Vectors, with the exception of an intron located 5′ of the chloramphenicol acetyltransferase (CAT) gene. The vector backbones were designed to increase expression of the reporter gene for easier monitoring of transcriptional activity in transfected eukaryotic cells. In addition, the pCAT®3 Reporter Vectors contain numerous features that aid in the structural characterization of the putative regulatory sequences.