Differences in transcription between transformed mouse cells in culture and the tumors that they produce in syngeneic mice.

RNA-DNA saturation hybridization experiments were used to determine the degree to which cellular DNA sequences are transcribed in cultured mouse cells transformed by polyoma virus and in tumors that develop after injection of these cells into syngeneic mice. A general, overall reduction in the proportion of the genome transcribed was found in tumors compared to the proportion in cultured transformed cells. When explants of the tumor cells were grown in culture, the level of transcription of both repetitive and nonrepetitive DNA returned to that observed in the original transformed cells.