sentences:  A computational model for model has been developed by Jean-Christophe Leloup and Albert Goldbeter to simulate the feedback loop created by the interactions between these proteins and genes, including the "per" gene and PER protein.The human homologs show sequence and amino acid similarity to Drosophila Per and also contain the PAS domain and nuclear localization sequences that the Drosophila Per have.The human proteins are expressed rhythmically in the suprachiasmatic nucleus as well as areas outside the SCN.