Figure 1: Breast Specific Retroviral Vectors 
(not drawn to scale: antisense regions are much shorter) 
The viral vectors shown above express the following genes 
under the control of a breast specific promoter (MMTV): 
either a tumor suppressor gene (RB), antisense against an oncogene 
(antisense c-fos, antisense c-myc), an easily assayed gene 
for control studies (CAT) , or antisense controls ("sense" c-fos 
and "sense" c-myc) . 
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