Excising recombination between double mutant lox and wild-type lox P in strongly Cre-expressing sub-lines. (a) Restriction endonuclease map of the targeted Ttr locus before (Ttr LacZ-KI allele) and after (Excised allele) Cre-mediated recombination. The pA signal of the mouse Pgk gene was used as a probe (indicated by the solid line). Fragment sizes are indicated. Bg, BglII; Sc, ScaI. (b) Southern blot analysis of Cre-expressing sub-lines. P represents the parental line before introducing the CAG-Cre-IRES-Hyg cassette. The numbers indicate passage numbers from the original cell stock. The positions of the bands from the nonexcised LacZ allele (LacZ), excised allele (Excised), and endogenous Pgk gene (Endo) are indicated by arrowheads. (c) Relative band intensities of the LacZ allele (hatched line) and excised allele (solid line) to the band intensities of the endogenous Pgk gene. The rate of excised band [ratio of excised band intensity to total (LacZ + excised) intensity] was calculated and is indicated by the gray line.