| Abstract: | ![]()
A comparison has been made between the activity of enzymes responsible for methylation of tRNA in a permanent line of adult Chinese hamster ovary fibroblasts maintained in in vitro culture, and that of cells derived from this line after exposure in vitro to the alkylating carcinogen N-nitrosomethylurea. A significantly elevated activity has been observed in several clones of cells which had received a single acute dose of the nitrosamide. A series of chronic treatments in which the single acute dose was given over a period of 8 weeks illustrated the cumulative effect of the fractionated doses on the methylase enzymes, and confirmed the repeatability of findings after a single acute dose. Evidence has been obtained from morphological criteria that a correlation appears to exist between the extent of morphological conversion within the cell population and the activity of the enzymes. Kinetic evidence suggests that this alteration in activity is not related to changes in growth rate alone. These results are discussed in relation to the concept that methylation of tRNA may relate to the degree of maturation and differentiation in a particular cell population. |
