This transgene contains a ubiquitously expressed pCAGG CMV enhancer/chicken beta-actin promoter, a floxed concatemer of three SV40 polyadenylation sites, and the human DMPK exon 15 containing 960 copies of interrupted CTG repeats (containing CTCGA after every 20 CTG repeats). The SV40 polyadenylation sites prevent expression of RNA from downstream genomic segments, and their removal by Cre-mediated recombination results in transcription and splicing of DMPK exon 15 into the transgene mRNA. Three lines were made, with the 1323 line showing the highest expression of mRNA from the recombined allele.