A specific example is the testing of drugs called aminoglycosides to treat cystic fibrosis and other diseases caused by premature termination codons, said Dietz. The idea is that these drugs would allow read-through of such codons, to generate adequate levels of full-length functional proteins. Unfortunately, these drugs have not performed very well, he said.

Our studies of the effects of one such drug on yeast indicate that this read-through generates mRNAs that trigger the nonstop decay mechanism to degrade them, said Dietz. This finding offers the promise that drugs that inhibit nonstop decay might enable aminoglycoside drugs to function as effective treatments for some genetic diseases.

Termination codons are present in about one-third of human disease genes, representing literally thousands of genes, said Dietz. So this dual-drug treatment strategy could be relevant to a large number of human disorders, including cystic fibrosis and muscular dystrophy.

In the second Science paper, lead author Ambro van Hoof, in Parkers laboratory, did experiments that revealed the specific cellular machinery that produces nonstop decay. According to Parker, those experiments showed that a multi-enzyme complex called the exosome is important for nonstop decay.

The exosome is a collection of enzymes called exonucleases that snip apart RNA molecules. In their experiments, van Hoof, Parker and their colleagues set out to see if the exosome was involved in nonstop mRNA decay.

It was known that the exosome was involved in a variety of RNA degradation processes in the cell, probably controlled through specific adapters, although we really dont understand the mechanisms well, said Parker. According to Parker, the adapter protein, which is attached to the exosome, somehow recognizes the nonstop RNA and attaches to the ribosome.

Parker, van Hoof
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Contact: Jim Keeley
keeleyj@hhmi.org
301-215-8858
Howard Hughes Medical Institute
21-Mar-2002