EVIDENCE THAT GENE AMPLIFICATION UNDERLIES ADAPTIVE MUTABILITY OF THEBACTERIAL LAC OPERON

Adaptive mutability is the apparent alteration in specificity or rate of mutability seen in bacteria during stress. A model is proposed by w hich gene amplification during selective growth can give the appearanc e of adaptive mutability without requiring any change in mutability. T he model is based on two assumptions, that a mutant lac locus with res idual function allows growth if its copy number is increased, and that true reversion events are made more likely by replication of chromoso mes with many copies of the locus. Apparent directed mutability, its r ecombination requirement, and its apparent independence of cell growth are all accounted for by the model. Evidence is provided far the requ ired residual function and gene amplification.