plays an important role in such a circadian mechanism. Its overexpression, in particular, causes DNA-damage induced apoptosis. In addition, down-regulation of PER1 can enhance tumor growth in mammals. PER1 also interacts with proteins ATM and Chk2. These proteins are key checkpoint proteins in the cell cycle. Cancer patients have a lowered expression of per1. Gery, et al. suggests that regulation of PER1 expression may be useful for cancer treatment in the future. Gene Orthologs The following is a list of some orthologs of the PER1 gene in other species: PER1 (Rattus norvegicus) PER1 (Mus musculus) per1a (Danio rerio) PER1 (Homo sapiens) lin-42 (Caenorhabditis elegans) PER1 (Bos taurus) per1b (Danio rerio) PER (Drosophila melanogaster) PER1 (Xenopus tropicalis) PER1 (Equus caballus) PER1 (Macaca mulatta) PER1 (Sus scrofa) Paralogs PER2 PER3 Location The human PER1 gene is located on chromosome 17 at the following location: Start: 8,140,470 Finish: 8,156,405 Length: 15,936 Exons: 24 PER1 has 19 transcripts (splice variants). Discovery The PER1 ortholog was first discovered by Ronald Konopka and Seymour Benzer in 1971. During 1997, Period 1 (mPer1) and Period 2 (mPer2) genes were discovered (Sun et al., 1997 and Albretch et al., 1997). Through homology screens with the Drosophila per, these genes were discovered. It was independently discovered by Sun et al. 1997, naming it RIGUI and by Tei et al. 1997, who named it hper because of the protein sequence similarity with Drosophila per. They found that the mouse homolog had the properties of a circadian regulator. It had circadian expression in the suprachiasmatic nucleus (SCN), self-sustained oscillation, and entrainment of circadian expression by external light cues. References External links More information on PER1 introns and exons Splice variants of PER1 Transcription factors PAS-domain-containing proteins