A. Ad-hERα and Ad-hERβ viruses were constructed as described in Materials and Methods using in vivo recombination in HEK-293 cells. The recombination occurs between the shuttle vector pACSK12-CMV5 carrying hERα or hERβ cDNAs and pJM17 adenoviral sequences. B. MDA-MB 231 cells were grown in 6-well plates and infected overnight with no virus (A), or Ad-GAL virus at MOI (multiplicity of infection) 1 (B), 10 (C), or 25 (D), 50 (E), 100 (F). β-galactosidase activity was monitored after 48 h of expression. The upper panel corresponds to a picture of the entire plate and the lower panel to a 200 fold magnification of each well.