Aphids (plant lice) and ants carry minibacteria that produce essential amino acids and vitamins. These minibacteria have very limited genetic material and many broken genes. Now, in an article in the journal Proceedings of the National Academy of Sciences, Uppsala researchers are presenting experimental findings that show that repeated errors in the conversion of DNA to protein save the function of the damaged genes.
Many insects, such as aphids, ants, and tse-tse flies are dependent on special minibacteria for their survival. These bacteria live isolated in special organs in the insects? bodies and are packed into their eggs to be spread to the next generation of insects. In this closed environment a great deal of genetic damage takes place, and the minibacteria?s genes are successively degraded.
Genetic damage arises during copying of the DNA string in the mother cell to the new DNA strings in the daughter cells. DNA is made up of four letters-?A, C, G, T. During copying of the same letter in a row, errors easily occur: for example, 10A can be erroneously copied as 9A or 11A or 12A. If such an error occurs in a gene, the reading frame is destroyed, and the gene loses its function. It is extremely uncommon for bacteria to have long series of the same letter in their genes. The minibacteria that live in insects, on the other hand, can surprisingly have hundreds of such regions in their genes. In several cases these regions have accumulated genetic mutations and the genes have popped out of their reading frame.
"Theoretically speaking, these damaged genes should no longer be able to function", says Siv Andersson.
In the new study, the scientists have shown that despite their damage these genes become protein. The secret lies in the fact that new errors occur during copying of DNA to RNA, so a mixture of RNA molecules with 9A, 10A, 11A, and 12A is formed. Owing to the new errors, in some cases the original damage is repaired, and the gene pops back into its proper reading frame so that protein can be created.
"The result is a robust but extremely inefficient system. The major share of the copied material is useless and will be degraded. But thanks to the small proportion that turn out right as a result of the repeated copying errors, the bacteria can survive, thereby making it possible for the aphids and ants to survive", says Siv Andersson.
These findings are of value to experiments being carried out around the world in attempts to use engineering to create minibacteria using artificial genetic material.
- Tamas et al. Endosymbiont gene functions impaired and rescued by polymerase infidelity at poly(A) tracts. Proceedings of the National Academy of Sciences, 2008; DOI: 10.1073/pnas.0806554105
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