 In some cell types, the photoreceptor protein cryptochrome (CRY) physically associates with TIM and helps regulate light-dependent degradation.CRY is activated by blue light, which binds to TIM and tags it for degradation.This ends the PER/TIM repression of the CLK/CYC-mediated transcription of "per" and "tim" genes, allowing "per" and "tim" mRNA to be produced to restart the cycle.