sentences:  Therefore, inhibition of CLK/CYC lowers "per" and "tim" mRNA levels, which in turn lower the levels of PER and TIM.Now, cryptochrome (CRY) is a light sensitive protein which inhibits TIM in the presence of light.When TIM is not complexed with PER, another protein, doubletime, or DBT, phosphorylates PER, targeting it for degradation.