In studies of breast cancer cells, [senior investigator Dr.
Bert] O'Malley and his colleagues showed how the clock works.
Using steroid receptor coactivator-3 (SRC-3), they demonstrated
that activation requires addition of a phosphate molecule to the
protein at one spot and addition of an ubiquitin molecule at
another point. Each time the message of the gene is transcribed
into a protein, another ubiquitin molecule is chained on. Five
ubiquitins in the chain and the protein is automatically
destroyed.A counter on a separate work tape: neat ! Main article
at sciencedaily; link via Science and Reason.