Common baker's yeast is helping a Utah State University biochemist learn how the instructions coded into the genes are translated into cell proteins.
Information Gayle Knapp is learning from these fungi is helping to change the standard way of looking at gene action. Understanding details of the RNA-protein system can also aid genetic engineers in their quest to manipulate gene expression.It has been thought that the "master molecule" DNA, which makes up the genetic material, stays inside the nucleus of the cell. Instructions coded in the genes, which are segments of DNA, are copied into messenger molecules known as RNA. The RNA messengers move outside the cell nucleus and direct the production of specific proteins, according to explicit instructions they have received.
But studies of yeasts are indicating that the messenger is not just a passive carrier of information, Knapp said.
Knapp began her work with yeast RNA about 10 years ago as a postdoctoral fellow at the University of California, San Diego. At that time, she said, curious segments of genes called introns had just been identified.
The introns are copied into the RNA when it is made. However, the introns are later cut out of the RNA. This snipping, or "editing," is necessary before the RNA will work correctly. The cell scissors are enzymes.
"An enzyme cuts out the intron, then the fragments are joined," Knapp said. "It's an incredibly precise removal, subject to controlled variation in the cell."
Knapp is focusing her studies on the site and method of intron removal. In the yeasts, one kind of RNA is processed at the nuclear membrane. She has found that mutant yeasts die because they are unable to process RNA.
Today, DNA has the distinction of being known as the master molecule. But billions of years ago, in the Earth's primordial soup, RNA was probably in charge, Knapp said.
Only recently have scientists turned their attention to the RNA intermediates, and they are not finding them dull. RNA adds to itself as well as subtracts. Its editing of the original message can be extensive.