In humans, circadian rhythms influence the sleep-wake cycle. They also affect other physiological processes such as nervous system activity, hormone production, blood pressure, appetite, digestion and body temperature. Even our mood and cognitive ability is influenced by it. Clock is a basic helix-loop-helix-PAS transcription factor that heterodimerizes with BMAL1. Together these transcription factors bind to E box elements (CACGTG) within the promoter of Period circadian genes (PER1 and PER2) stimulating their transcription. CRY1 is a critical component of the circadian oscillator that represses CLOCK-BMAL1 mediated transcription when translocated into the nucleus. PER1, also known as RIGUI, influences circadian rhythms by interacting with, and stabilizing, other circadian regulatory proteins.