A MUTATION AMPLIFYING THE GENES CARRIED BY THE Pi-HISTIDINE PLASMID

A spontaneous mutation of the pi -histidine plasmid has been isolated that causes increased expression of the histidine genes and the gnd gene which are normally present on the plasmid. Transduction frequency and F-mediated conjugational transfer of the mutant plasmid indicate gene amplification has occurred without an increase in the number of replicating units. A model for gene amplification dependent upon insertion sequences is proposed to explain the mutant phenotype.