Fig. 1. Retroviral vectors used for cell immortalization. Proviral forms after genomic integration are shown. The E6/E7 genes were cloned between a 5' HindIII site and a 3' XhoI site. A, E6/E7 expression is driven by the SV40 internal promoter. A tissue-specific internal promoter of the aortic -SM actin gene (B) or under the retroviral promoter LTR (C) is shown. The neor gene expression was placed under the retroviral promoter or under the internal promoter.