3 PERIOD HOMOLOGS IN MAMMALS - DIFFERENTIAL LIGHT RESPONSES IN THE SUPRACHIASMATIC CIRCADIAN CLOCK AND OSCILLATING TRANSCRIPTS OUTSIDE OF BRAIN

We have cloned and characterized the mouse cDNA of a third mammalian h omolog of the Drosophila period gene and designated it mPer3. The mPER 3 protein shows similar to 37% amino acid identity with mPER1 and mPER 2 proteins. The three mammalian PER proteins share several regions of sequence homology, and each contains a protein dimerization PAS domain . mPer3 RNA levels oscillate in the suprachiasmatic nuclei (SCN) and e yes. In the SCN, mPer3 RNA levels are not acutely altered by light exp osure at different times during subjective night. This contrasts with the acute induction by light of mPer1 and mPer2 RNA levels during earl y and late subjective night. mPer3 is widely expressed in tissues outs ide of brain. In liver, skeletal muscle, and testis, mPer RNAs exhibit prominent, synchronous circadian oscillations. The results highlight the differential light responses among the three mammalian Per genes i n the SCN and raise the possibility of circadian oscillators in mammal s outside of brain and retina.