AbstractProperties of the change from asparagine dependence (asn‐) to independence (asn+) were investigated in the androgenetic haploid frog cell line ICR 2A. Two types of asn+variants arose spontaneously during culture. Glutamine‐dependent asparagine synthetase (AS) activity, found to be deficient in asn‐ cells, was repressed by asparagine in one type of variant and expressed constitutively in the other. No quantitative differences in AS‐specific DNA sequences or changes in ploidy were evident between asn+and asn−cells. The asn‐ frequency in ICR 2A populations, not dramatically influenced by chemical mutagens, was increased 130‐fold by exposure to 5‐azacytidine. The methylation of CCCG sequences at the 5′ end of the AS structural gene was found to be reduced equally in both types of asn+variant. These results indicate that decreased DNA methylation is essential but not necessarily sufficient for the expression of AS activity in this
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