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Contribution of the inactivation of checkpoints to Ras transformation. Model of how the progressive loss of checkpoints allows Ras to act positively on the cell cycle. Loss of p53 activity causes Ras to be proliferative in the absence of mitogens. Inactivation of the Rb family, by loss of p16INK4A or by inactivation by the N terminus of SV40 LT, renders the cells capable of proliferation independently of anchorage and insensitive to contact inhibition.
