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