Cotransfection problems - (Feb/08/2002 )

I`m performing transfections in the DLR using promoter contructs in pGL3-basic  and pRL-TK and this works fine.
For example SV40 has an 30fold induction compared with Basic.
But when I trie to cotransfect with expression plasimds, the activity of pGL3 Basic  as well as TK is induced. Example the induction of SV40 compared with Basic is now only 4-fold.

Has anyone a explanation  or a suggestion to solve this problem?

Are you sure your pGL3 is induced instead of your SV40 repressed because you are cotransfecting too much expression plasmid with CMV promoter? If you do this there will be competition for RNA polymerase by the strong viral promoters and  overall levels of transcription will drop.