The isolation and characterization of asparagine-requiring mutants of Chinese hamster cells☆

Abstract Nine asparagine-requiring mutants were isolated in culture from the Don line of Chinese hamster cells. Investigation of the asparagine requirements of the mutants, the effect of asparagine deprivation on macromolecular synthesis, and the rates of reversion to asparagine independence indicated that there were differences between the mutant clones. Biochemical analysis revealed that the defect in the mutants was due to a deficiency of the enzyme asparagine synthetase, and that the enzyme activity in the mutants and Asn + revertants obtained from them was not influenced by the concentration of asparagine in the growth medium. Complementation analysis by Sendai virusmediated cell fusion indicated that the lesion behaved as a recessive trait, and was probably located in the same gene in all the mutant clones.