The targeting construct introduced a floxed STOP cassette followed by a mVenus and the ubiquitylation domains of human GMNN (amino acids 1 to 110) fusion. Cre-mediated recombination remvoed the STOP cassette. This fluorescent ubiquitylation-based cell cycle indicator accumulates in the nuclei during the S/G2/M phases of the cell cycle. (J:196795)