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New option in gene expression.

As scientists have described the details of the cellular mechanics of gene expression, they have been impressed again and again with the versatility and thriftiness of the process. The most striking discovery was that genes contain noncoding segments (introns) interspersed among coding segments (exons), both introns and exons are copied into messenger RNA, and then the introns are removed from the RNA. Variations in this RNA modification, called splicing, allow the cell to use a single gene to code for more than one protein. A DNA segment can be used as an intron in some cells and as an exon in others, dramatically altering the restaurant protein. But all the spliced RNA molecules examined seemed to be the result of the simple deletion of introns from a single gene. The exon of one gene was never joined to an exon of another.

Now two laboratories report the first evidence that, at least in test tube experiments, the splicing procedure may be "promiscuous," combining exons from various genes. The scientists suggest that such "trans splicing" occasionally may occur naturally, perhaps to distribute a single exon to many different messenger RNA molecules. For example, in the parasites called trypanosomes, the same short RNA segment appears at the end of many messenger RNA molecules but does not appear in the corresponding genes.

Experiments indicating the existence of trans splicing were reported in the August CELL by David Solnick of Yale University and by Maria M. Konarska of the Polish Academy of Sciences in Warsaw and Richard A. Padgett and Phillip A. Sharp of Massachusetts Institute of Techonology. In each set of experiments, RNA exons (each attached to an intron) fro two different genes were mixed together. The tans splicing was greatest when the introns shared part of the RNA sequence. But Sharp and his colleagues also report a low level of trans splicing when there was no shared intron sequence. The scientists speculate that cells must have a powerful mechanism to suppress such splicing under most conditions.
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Title Annotation:trans splicing
Publication:Science News
Date:Sep 14, 1985
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