I am going to express three genes in mammalian cells, one of them is a selection marker. I am doing this based on the opinion that if all genes are expressed under one promoter the chance of false possitive clones (due to the damage to GOI unit and integration of the selecetion marker unit only ) will reduce. and also I need to have proportional expression of the other two genes as well. So I was wondering if any one has expirences with IRES, 2A or both of them. my current design is based on IRES. any suggestion would be highly appreciated.