The pRL-CMV Vector may be used in combination with any experimental reporter vector to co-transfect mammalian cells. However, it is important to realize that trans effects between promoters on co-transfected plasmids can potentially affect reporter gene expression . Primarily, this is of concern when either the control or experimental reporter vector, or both, contain very strong promoter/enhancer elements (such as CMV). The occurrence and magnitude of such effects will depend on several factors: a) the combination and activities of the genetic regulatory elements present on the co-transfected vectors, b) the relative ratio of experimental vector to control vector introduced into the cells, and c) the cell type transfected.