A Temperature-Sensitive Mutant of CHO-K1 Cell Arrested in the G2 or Late S Phase

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Abstract
A new type of temperature-sensitive mutant, 11C3 was isolated from chinese hamster ovary CHO-K1 cells and partially characterized. At a nonpermissive temperature the number of mutant cells hardly increases. Incubating mutant cells first at a nonpermissive temperature (39.degree. C) for 24 h reduces the plating efficiency to 1/3 that found without prior incubation. DNA synthesis slows down gradually for 30 h at 39.degree. C, but protein synthesis does not decrease until 48 h after the shift up. Analysis of the DNA content of the individual cells shows that the proportion of cells containing the 4.degree. C amount of DNA markedly increases in 28 h after the temperature is shifted up. Light microscopy shows that mitotic figures decrease during this period and that the cells become large and flat with a single large nucleus. Experiments on synchronized cell populations suggest that although the temperature sensitive period exists in the S-phase, cells are arrested near the end of the S-phase or in the G2-phase. The colchicine binding assay revealed that the colchicine binding protein in mutant cells increased during incubation at a nonpermissive temperature. This supports the results described above.