sentences:  NPAS2 has been shown to form a heterodimer with BMAL1 in both the brain and in cell lines, suggesting its similarity in function to the CLOCK protein in this TTFL.Compensation is a key feature of TTFLs that regulate circadian rhythms.BMAL1 compensates for CLOCK in that if CLOCK is absent, BMAL1 will upregulate to maintain the mammalian circadian rhythms.