Abstract
Nutritionally deficient cells were detected and isolated from cultures of Chinese hamster hai cells by our replica plating method. The nutritionally sufficient characteristics (Ala+, Asn+, Pro+, Asp+, Hyp+) of a prototrophic clone isolated in the first survey, which was performed about one month after the cells were transferred to the complete medium from the original medium, were stable. On the other hand, the majority among the nutritionally deficient characteristics (Ala-, Asn-, Pro-, Ser-, Gly-, TdR-) of an auxotrophic clone isolated in the second survey, which was performed about one year after the cells were transferred to the complete medium, were unstable. Only the thymidine-deficient characteristics of this clone were stable, and the mean reverse mutation frequency of this characteristic was 4.7×10-6. These results indicate that epigenetic as well as genetic changes may be related to the changes in nutritional requirement of mammalian cells and that our replica plating method might equally detect the cells having apparently genetic characteristics altered by epigenetic as well as genetic changes.
