Calcium requirements for the proliferation of cells infected with a temperature-sensitive mutant of Rous sarcoma virus.

Between 32 degrees and 39 degrees, uninfected normal rat kidney (NRK) cells proliferated minimally, or not at all, in medium containing 0 to 0.01 mM extracellular free calcium. Transformation of NRK cells by wild-type avian sarcoma virus B77 enabled them to proliferate equally rapidly at all temperatures in high (1.25 mM)- or low (0.001 mM-calcium medium. Transformation by the temperature-sensitive LA-23 mutant of Rous sarcoma virus also enabled NRK cells to proliferate in low (0.001 mM)-calcium medium at 32 degrees or 37 degrees. However, the LA-23 NRK cells could not proliferate in low (0.001 mM)-calcium medium at a nonpermissive temperature such as 39 degrees, which prevents expression of other aspects of the transformed phenotype.