A. Schematic diagram of the pCL constructs. The parental pCL vector encodes no inserted cDNA. The pCLp16, pCLp53 and pCLRb vectors contain the p16INK4a, wild-type p53, and Rb cDNA's, respectively . The expression of the neomycin phosphotransferase gene (Neo) is driven by the SV40 promoter. B. Colony formation in C6 cells was inhibited by p16. C6 cells were transduced with the indicated pCL viral supernatant prior to selection with G418. The number of colonies resulting from pCL infected cells was defined as 100%. The number of colonies formed after infection with the other pCL viruses and G418 selection is presented as the percent of colonies as compared with the control. The data presented is the average of at least three independent experiments with the standard deviation indicated by the error bars.