Transfections...?

[Eric Tsai]

Hi, everyone!

I have a question about subsequent transfections.  I am using,
primarily, the neomycin gene (G418).  I would like to follow this with a
secondary transfection using the psv2gpt gene (mycophenolic acid, etc). 
As far as selection medium following the first transfection, I would
ordinarily maintain my transfectants in low dose G418.  If I am  doing a
second transfection, would my selection medium contain both G418 and the
resistance reagents for psv2gpt and would my final maintenance medium
also contain reagents for both resistances? ( I am not even totally
convinced that the maintenance of stable expression depends on low dose
G418).  Any help would be appreciated!