Abstract
The stability of the repressor of alkaline phosphatase specified by the R1+ regulator gene was determined by studying the decay of repression after elimination of this gene. The gene is eliminated from R1 /R1-heterogenotes by the production of Rl" homogenotes, a process which is powerfully stimulated by thymidylate starvation. The lifetime of the R1+ repressor is somewhat under 0.3 generations, assuming that the differential rate of enzyme synthesis varies inversely with the first power of repressor concentration. Evidence in support of this assumption is adduced from the variation in differential rate with dosage of the R1+ gene.