Gene Expression Clocks

A EurekAlert article entitled Clocking in and out of gene expression contains the following opening paragraphs (in red).

HOUSTON (June 15, 2007) – A chemical signal acts as time clock in the expression of genes controlled by a master gene called a coactivator, said Baylor College of Medicine researchers in a report that appears in the journal Cell today.

“We have long known that our bodies live by a daily and monthly and even yearly clock and that cells have clocks as well,” said Dr. Bert O’Malley, chair of molecular and cellular biology at BCM and senior author of this report. “We have actually taken this concept to the gene now and said that we are made up of 25,000 genes that have clocks too.” Genes get expressed and carry out their functions through proteins, he said. Gene expression involves the machinery of the cell translating the gene’s code into a protein that carries out function. This process has to have a beginning and an end.

Gene expression is time regulated and O’Malley indicated that master genes or coactivators determine when genes will be expressed. The regulating clock can be triggered by post-translational modifications of steroid receptor proteins. Ubiquitinylation is one such modification strategy. Successive ubiquitins are added correlating to the transcription of gene messages into proteins. A chain of five ubiquitins causes the destruction of the protein. Some more from the article:

“It’s built-in self destruction,” said O’Malley. “It prevents you from activating a potent factor in the cells that just keeps the clock running and the gene continuing to be expressed.” In that scenario, the result could be cancer, too much growth or an abnormal function.

“It means there’s a fixed length of time that the molecule can work. When it’s activated, it’s already preprogrammed to be destroyed. The clock’s running and each time an ubiquitin is added, it is another tick of the clock.” When the clock system fails, problems result.