FIG. 1.

Morphological change of OS7-2 cells by temperature shifting. F2408 is a rat fibroblast cell line established from REF of Fisher rat (13). S7-1 is an F2408 cell line transformed by the SR-D strain of RSV (23). OS7-2 is an F2408 cell line containing a temperature-sensitive mutant (OS122) of RSV (38, 39, 54). The cells were cultured in Dulbecco’s modified Eagle’s medium supplemented with 5% FCS (growth medium). OS7-2, S7-1, and F2408 cells were inoculated into plastic dishes containing growth medium and incubated at 35°C (permissive temperature). After incubation for 24 h, the culture temperature was increased to 39°C. At 0, 4, 8, 12, 16, 20, and 24 h after temperature shifting (0 and 24 h for S7-1 and F2408), cell morphologies were observed with a phase-contrast microscope and photographed.