ESTIMATION OF MUTATION RATES WITH MAMMALIAN CELLS IN CULTURE

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Abstract
The isolation and some properties of cultured mammalian cells (AMK 2-2) heritably resistant to metabolic analogues was previously reported (Proc. Natl. Acad. Sci. USA 45(6): 867-872. 1959). With puromycin, low resistance (Pmr-1) and higher resistance (Pmr-2) mutants were obtained from the parent (Pms) in at least two sequential mutational events. The present report details the procedure and evidence for the validity of mutation rate measurements. The mutation rates from Pms to Pmr-1 and from Pmr-1 to Pmr-2 were estimated by the classical method of Luria and Delbruck, to be approximately 4 x 10-6 and 1 x 10-4 mutations per cell per generation, respectively. In addition, the heritable increases in puromycin resistance are not dependent upon the presence of the antibiotic. Whether the changes result from genic or chromosomal alterations cannot yet be determined.