Rous sarcoma virus SRC gene expression on the growth of quail embryo skin fibroblasts and the establishment of permanent cell lines.

Permanent cell lines of Quail embryo fibroblasts appear in cultures of cells infected with a wild type strain of Rous sarcoma virus (SR-RSV) or with its temperature sensitive transformation mutants (ts-T) (NYts68 and PA101) following a three step process. In step one, infected cells grow twice as fast as the control. The second step consists of a crisis during which the cell population is stationary for four to five weeks. Towards the fourth week several foci of cell growth are observed in the flasks. Respreading of the content of these flasks yields permanent lines. This constitutes the third step of the population evolution. In step one the growth rate of the infected cells is the same irrespective of the incubation temperature (36 degrees C or 41 degrees C) whereas the level of the pp60v-src activity is considerably depressed at 41 degrees C for NYts68 and PA101. Foci do not appear at restrictive temperature in the ts infected population and permanent lines are not recovered under that condition. These lines grow ony at 36 degrees C. It can be shown that the virus which they produce is not modified with respect to the temperature sensitivity of the src gene expression since newly infected fibroblasts grow equally well in step one at both 36 degrees C and 41 degrees C, and stop after the same number of generations. This finding suggests that the events which, during the crisis period, lead to the establishment of permanent lines, take place at the cellular level but depend on the activity of the pp60v-src protein for their occurrence or their expression.