I'm trying to perform a reporter assay using multiple plasmids. In short, I want to see if a combination of TFs activates my reporter. I have my system working well with one plasmid and my positive control reporter. However, when I express all 7 plasmids (Renilla, firefly, and 5 TF expression constructs) required for the experiment, my positive control no longer works, and I'm unable to detect expression of my transfected plasmids by western. I am using the same amount of DNA for my positive control (bringing up total DNA concentration with empty vector) and the experimental transfection. ANy suggestions on how to begin optimizing this system? Is the expression of 7 plasmids even realistic (I'm using U2OS cells)? Thanks!