Figure 1.

The Tet^S phenotype is the result of Tn10 loss or DNA amplification of Tn10 sequences. (A) Agarose gel electrophoresis of total DNA isolated from late Lac⁺ Tet^S cultures digested with BglI and stained with ethidium bromide. M, λ BstEII size marker; lane 1, FC40; lanes 2–6, late Lac⁺ and Tet^S revertants. (B) Southern blotting of the gel presented in A, hybridized with the IS10R probe shown in C. (C) Schematic of Tn10. The arrows represent the IS10 inverted sequences, left and right, respectively. The thick line represents the IS10R probe used in these experiments. (D) Assessment of Tn10 sequences among the Lac⁺ revertants. Panel I is an autoradiograph of total DNA obtained by in situ lysis of late Lac⁺ revertants picked directly from selective plates and hybridized to a MutY probe. Panel II depicts the same samples shown in Panel I, but hybridized to an IS10/Tet/Kan probe.