The transgene comprises bacterial artificial chromosome (BAC) RP24-277K16 containing the mouse period 1 (Per1) gene into which a Venus-NLS-PEST fusion gene has been inserted. Venus is a yellow fluorescent protein enhanced by the introduction of five point mutations. To improve the protein's kinetics, the PEST domain of the mouse ornithine decarboxylase gene was introduced following the penultimate codon of the gene. A nuclear localization signal (NLS) was cloned in-frame between the Venus coding sequence and the PEST domain. The sequence encoding the fusion protein is preceded by a human cytomegalovirus (hCMV) promoter and followed by an SV40 polyadenylation signal. Its robust expression in a population of cells in the suprachiasmatic nuclei (SCN) of the hypothalamus is cyclic and light-inducible; it is also widely expressed in neuronal and non-neuronal cells of brain regions outside the SCN. (J:150729)