MUTATIONS CAUSED BY INSERTION OF GENETIC MATERIAL INTO GALACTOSE OPERON OF ESCHERICHIA COLI

Density-gradient analysis shows that λ transducing phages which carry spontaneous extreme polar mutations of the galactose operon have higher buoyant densities than otherwise identical phage which carry a wild-type galactose operon. Control experiments show that the density increases are not artifacts of the techniques used to isolate mutant transducing phages and that removal of the spontaneous extreme polar mutations by reversion or recombination leads to a loss of buoyant density. The simplest explanation for these results is that the mutations analysed are the consequences of the linear insertion of foreign DNA into the E. coli galactose operon. The insertion hypothesis provides an explanation for the strong polarity and unusual genetic properties of spontaneous extreme polar mutations. © 1969.