SV-40 promoter

[L.Y.Chau]

Hi,
I am doing transfection exp. on undifferentiated and DMSO-induced 
differentiated HL-60 cells.  The B-gal activity driven by SV-40 promoter is 
always 3-fold lower in differentiated HL-60.  Here comes the question!  Is 
SV-40 promoter down-regulated in differentiated cells?  If I need to 
normalize my transfection data, is there any other promoter I can use which 
is not regulated during differentiation?

Jonghwei