Bacterial factories for small receptors.

Scientists think that an animal's complex sense of smell is based on the activities of thousands of individual receptors, each responsible for detecting a particular odor and relaying that information to a specific area of the brain. Studies of genes that code for these receptors have boosted this theory.

Yet despite "a lot of very compelling inferential evidence, there has not been a demonstration that one of these molecules actually is an odor receptor," says Glenn R. Prestwich of the University of Utah in Salt Lake City (SN: 8/4/90, p. 79). Now, he and his colleagues at Stockholm University and the University of Hohenheim in Stuttgart, Germany, report in the Dec. 17 Biochemistry that they've found a smell receptor that matches a specific odor. The researchers inserted a gene from rats into bacteria that have the potential to produce the rat receptor in abundance. The receptor interfered with the bacteria's growth, however, so Prestwich and his colleagues had to create a slightly modified form of the receptor that the bacteria could synthesize in large quantities without ill effect.

Then, by methodically testing various smells, the researchers found two molecules, called lilial and lyral, that bound well to the receptor. Prestwich describes each of the compounds as having "sort of a floral odor." The next step will be to determine which part of the receptor the odor molecules bind to, a search made easier now that bacteria can make as much receptor as the researchers need. The technique should also enable scientists to make a class of similar receptors in large amounts.