CIRCADIAN OSCILLATION OF A MAMMALIAN HOMOLOG OF THE DROSOPHILA PERIODGENE

Many biochemical, physiological and behavioural processes in organisms ranging from microorganisms to vertebrates exhibit circadian rhythms( 1). In Drosophila, the gene period (per) is required for the circadian rhythms of locomotor activity and eclosion behaviour(2). Oscillation in the levels of per mRNA and Period (dPer) protein in the fly brain i s thought to be responsible for the rhythmicity(3,4). However, no per homologues in animals other than insects have been identified. Here we identify the human and mouse genes (hPER and mPer, respectively) enco ding PAS-domain (PAS, a dimerization domain present in Per, Amt and Si m)-containing polypeptides that aro highly homologous to dPer. Besides this structural resemblance, mPer shows autonomous circadian oscillat ion in its expression in the suprachiasmatic nucleus, which is the pri mary circadian pacemaker in the mammalian brain(5,6). Clock, a mammali an clock gene encoding a PAS-containing polypeptide(7,8), has now been cloned: it is likely that the Per homologues dimerize with other mole cule(s) such as Clock through PAS-PAS interaction in the circadian clo ck system.