The transgenic construct has the Pgk1 promoter and the EGFP gene separated by a floxed STOP cassette containing a puromycin resistance selection marker, two poly A sites and a trasncriptional pause cassette (synthetic pA site and a transcriptional pause site). The linearized construct was electroporated into E14TG2a subclone IV ES cells. Positive clones were injected into day 3.5 C57BL/6 blastocysts and chimeras were bred to C57BL/6 mice to establish the transgenic line. (J:135901)