I have been trying to express protein in HeLa cell with pcDNA3.1 mammalian expression vector. I had to use his-tag at c terminal of my target protein since my protein cant be detected with suitable antibody. The problem is I found very low expression of my protein. I checked also with Ds-Red system and saw expression under microscope but it is low. Can anybody suggest me some strong mammalian expression system to increase my protein expression?? I was thinking of pMEX-HA expression system..any idea? Thanks in advance.