Comparison of the ability of K-Ras–transformed immortalized Rce1α/α and Rce1flx/flx fibroblasts to form colonies in soft agar. Rce1flx/flx fibroblasts were infected with a K-Ras retrovirus, then treated with either lacZ adenovirus or Cre adenovirus. In Rce1flx/flx cells treated with Cre adenovirus, the Rce1 was fully deleted, generating Rce1α/α fibroblasts. In each experiment, the excision of Rce1 resulted in fewer colonies in soft agar (P = 0.029, P = 0.005; P = 0.09; P = 0.008). Reproduced, with permission from Molecular and Cellular Biology (Bergo et al., 2002a).