Jensen rat sarcoma cells in culture require L-asparagine for growth and lack detectable levels of asparagine synthetase. Cultures exposed for 24 h to graded concentrations of 5-azacytidine give rise to asparagine-independent variants in high frequency. These prototrophs are stable phenotypically whether maintained in the presence or absence of L-asparagine. Asparagine synthetase activity in several variant clones was uniform in thermolability and several kinetic parameters, as well as in immunological properties. Parental Jensen rat sarcoma cells contained no detectable immunologically cross-reacting material VSports手机版. Our data suggest that transitions between asparagine dependence and independence in these cells are mediated by stable shifts in gene expression rather than by structural gene mutations. .