Expression of a dominant negative mutant of Myc impairs soft-agar colony formation by TEL/PDGFRβ. The Rat-1 expressing dominant negative mutants of Myc (MycRX, Max2RX) and transfected with the TEL/PDGFRβ vector or the control vector were plated in soft agar and the formation of colonies was assessed after 2 weeks of culture. (a) Rat-1 MycRX/Max2RX, (b) Rat-1 MycRX/Max2RX expressing TEL/PDGFRβ, (c) Rat-1 Max2RX, (d) Rat-1 Max2RX expressing TEL/PDGFRβ, (e) Number of colonies per dish. Only the colonies < 0.3 mm were counted. This is representative of three independent experiments.