TEMPERATURE-SENSITIVE MUTANT SHOWING 2 DEFECTIVE FUNCTIONS

  • 1 January 1978
    • journal article
    • research article
    • Vol. 48  (2) , 155-165
Abstract
A temperature-sensitive growth mutant, 13B11 (derived from CHO[chinese hamster ovary]-K1 was partially characterized. Upon shift to the nonpermissive temperature (39.degree. C) DNA synthesis slows down, but is partly resumed after prolonged incubation at 39.degree. C. Reduction in the rate of DNA synthesis apparently is mainly due to decrease in the proportion of DNA synthesizing cells; the increase in the rate observed afterwards is due to appearance of cells that enter S. Synchronized mutant cells incubated at 39.degree. C from the beginning of G1 enter S with the delay of 6 h. By incubating the cells at 39.degree. C for a restricted period during the G1 phase, some processes in late G1 are found to be susceptible to the high temperature. Mutant cells shifted up in the middle of S performed cell division; cells up-shifted in G1 phase did not, although about half of these cells divided when they were shifted down in the presence of hydroxyurea. The analysis of DNA content of the cells cultured at 39.degree. C for more than 1 generation time revealed the accumulation of nuclei containing DNA in amount of almost 4C level. In this mutant the process necessary for cell division is also temperature-sensitive. Considering the frequency of the appearance of spontaneous revertants (2 .times. 1016), the apparent 2 lesions of this mutant might be ascribed to the single mutation.