Highly purified. Control Peptide for P3342-01 (affinity purified antibody) and P3342-01B (antiserum) Several endogenous factors have been linked to rhythmicity or circadian behavior of living organisms. In Drosophila, the genes period (dPer) and timeless (tim), and in Neurospora frequency (frq), have been proposed to be responsible for their circadian rhythm. Human and mouse genes encoding a basic helix-loop-helix (bHLH) and Per-ARNT-Sim (PAS)-domain with significant similarity to the Drosophila Period have been reported. The cDNA sequences of hPER and mPer1 (also named RIGUI) are predicted to encode for proteins of length 1290 and 1291 amino acids respectively. Homologues of mPer1 designated Per 2 (1257aa) and Per3 (1113aa) have also been cloned. Both Per1 and Per2 levels show circadian rhythm in the SCN and eyes. It has been suggested that mPer regulates neuronal activity in the SCN. Using genetic approach, a single mutation of A to T in the Clock gene affects circadian rhythmicity i