which of the five proteins are \"transcription factors\"? The genes that control

Question

which of the five proteins are "transcription factors"?

The genes that control The circadian clock are regulated by two nuclear proteins, PER and TIM, that slowly accumulate and then bind to one another to form dimers. When PER and TIM accumulate enough to dimerize, they enter The nucleus and shut off The expression of circadian genes including themselves. They do so by inhibiting CLOCK and CYCLE, which stimulate The transcription of per and tim genes. PER is highly unstable; most of The protein is degraded so quickly that it never has a chance to repress CLOCK-dependent pertran- scription.The degradation of PER is regulated by at least two different phosphorylation events by different protein kinases. When PER binds to TIM, PER is protected from degradation. As CLOCK drives more and more per and tim expression, enough PER and TIM eventually accumulate that The two can bind and stabilize each other, at which point they enter The nucleus to repress their own transcription. As a result, per and tim mRNA levels fall; thereafter, PER and TIM protein levels fall and CLOCK can (once again) drive expression of per and tim mRNA. During daylight TIM protein is degraded by signaling pathways that are regulated by light (including cryptochrome), so PER/TIM complexes form only at night. The CLOCK protein induces PER and TIM expression but is inhibited by PER and TIM proteins

Explanation / Answer

PER, TIM, CLOCK, CYCLE and cryptochrome.

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