SUMMARY: A large number of spontaneous conditional revertants of glutamine auxotrophs were isolated by plating cells on minimal medium and incubating them at various temperatures. No heat-sensitive revertants were found among 2000 scored; however, revertants with a cold-sensitive glutamine requirement were quite common. Growth of the latter class ceased immediately upon transfer to the restrictive temperature implying that glutamine synthetase activity was affected. Mapping data are consistent with a genetic location in or near , the structural gene for glutamine synthetase, for all cold-sensitive revertants tested. These revertants are likely to have second site suppressor mutations in since many have altered levels or kinetics of glutamine synthetase activity or a changed pattern of feedback inhibition.


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