[Isolation and characteristics of temperature sensitive mutants in a culture of Chinese hamster cells].

The treatment of a temperature-resistant glutamine-independent clone of Chinese hamster cells (237 glu+ tr) with 5-bromodeoxyuridine (BUdR) for 48 or 72 hours at 40 degrees C and subsequent illumination with visible light was used for selection of spontaneous and N-methyl-N'-nitro-N-nitrosoguanidein-induced ts mutants. 30 clones were isolated. Their temperature-sensitivity was studied at two cell densities: 500 and 10000 (or 15 000) cells per dish. 21 clones proved to be temperature-sensitive. The expression of temperature-sensitivity of 11 clones was independent of cell densities used. The remaining 10 clones could be divided in two groups: those expressing temperature-sensitivity only at low plating inoculum (6 clones) and those temperature-sensitive at 10 000 (15 000) plated cells per dish (4 clones). Possible mechanisms of this phenomenon are discussed. Most isolated clones behaved as leaky mutants. Isolation of ts clones without special mutagen treatment from a tr cell population after its permanent incubation at 40 degrees C, restrictive for ts cells, is regarded as strong evidence in favour of the mutagenic effect of BUdR and visible light.