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No. 139: Jan-Feb 2002

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How The Genome's Message Can Be Altered

Our genomes (complements of genes) can no longer be called sets of instructions like those in a computer program. Demonstrating the veracity of this statement are the following three quotations.

Increasingly, a picture of interactivity and multifunctionality among genes is emerging that precludes such a simple one-to-one mapping. Furthermore, the genome can exhibit considerable flexibility to adapt when the expression of a particular gene fails, and the interpretation of a mutant phenotype [life form] is also less trivial than it may seen. "Not only are behavioural phenotypes very sensitive to non-genetic influences," writes [R.] Greenspan, "but also the highly interconnected network of the nervous system sets up an additional layer of complexity between the gene and the realization of the phenotype." (Ref. 1) Many genes code for multiple variants of the same protein. And many proteins are modified by adding sugar molecules, which play a big role in determining where proteins go and what they do. What's more, different proteins can join together to carry out completely new functions. (Ref. 2)

A group of French biologists, led by Francois Jacob and Jacques Monod showed that the gene's boundaries are fuzzier than had been thought and that genes are not restricted to chromosomes.

Recently, biologists have found genes within genes, overlapping genes, and DNA sequences that specify one protein when read "forward" and another when read "in reverse."

Muddling things further, the instructions encoded in the DNA do not always reach the ribosome as a literal translation. In a phenomenon known as RNA editing, an enzymatic highwayman intercepts the RNA message en route and alters it, so the resulting protein is not identical to that specified by the DNA. (Ref. 3)

We can sum up by saying that a lot can happen to that information encoded in the genome before it is put to use.

References

Ref. 1. Anonymous; "The Flexible Genome," Nature, 411:xi, 2001.
Ref. 2. Coghlan, Andy; "Privatising Your Proteins," New Scientist, p. 5, April 14, 2001.
R3. Comfort, Nathaniel C.; "Are Genes Real? Natural History, 110:28, June 2001.

From Science Frontiers #139, Jan-Feb 2002. 2001 William R. Corliss

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