Gt(ROSA)26Sor^tm1Etz

A vector, which contains (5' to 3') a splice acceptor, floxed neo/stop cassette and sequence encoding mutated nuclear localized lacZ with intragenic duplication corresponding to nucleotides 870-1987 after the ATG such that a shift in codon phase introduces a TGA STOP codon at nucleotide 1993 was inserted into the locus via homologous recombination. The duplication in the lacZ sequence truncated b-galactosidase molecule making the lacZ inactive, except in small fraction of cells undergone infrequent spontaneous random intragenic homologous recombination restoring the functional lacZ sequence. (J:278250)