"In the nucleus, the DNA sequence of a clock gene is transcribed to mRNA; the resulting message is exported from the nucleus, translated into a clock protein, and is then modified. This clock protein is itself part of the molecular machinery that controls the transcription of its ‘own’ gene. When enough clock proteins have been made, they are imported back into the nucleus, where they start to inhibit the transcription of their own mRNA. Once this inhibition is strong enough, no more mRNA molecules are transcribed, and the existing ones are gradually destroyed. As a consequence, no more proteins can be produced and the existing ones will also gradually be destroyed. When they are all gone, the transcriptional machinery is not suppressed anymore, and a new cycle can begin."