Contains a genomic fragment that encompasses PNUTS, in which the coding sequence is wild-type and is tagged at the C-terminal end with EGFP followed by a stop codon. A second copy of the PNUTS 3' exon is present downstream of this wild-type transcription unit; this duplicated exon carries a W726A amino acid substitution and is tagged at the C-terminal end with mCherry. Two FRT sites are present, one in the large intron upstream of the EGFP-tagged, wild-type 3' exon and one downstream of the stop codon that follows the EGFP tag. In the absence of FLP recombinase, the expressed PNUTS protein contains the EGFP-tagged wild-type 3' exon and the duplicated, mutated 3' exon is not expressed. In the presence of FLP recombinase, the EGFP-tagged wild-type 3' exon is excised, and the duplicated 3' exon is incorporated into the expressed PNUTS protein, resulting in expression of a mutant protein that carries a W726A amino acid substitution and is tagged at the C-terminal end with mCherry.