Research performed by: Anne-Laure Chateigner-Boutin and Maureen R. Hanson
While some RNA editing sites require a lot of surrounding sequences, others require a minimal amount. For each one of these individual editing sites, there are various specific trans-acting elements that are used during regulation of a different target gene. Researchers gathered that if each editing site were independent, more than 400 proteins would be necessary for successful recognition of the editing site by the organelle. In order to test this theory of independence of the editing sites in chloroplasts, the researches conducted an experiment in which they carefully observed the degree of editing in thirty-one known tobacco chloroplast editing sites in two different tobacco lines, both of which contained plastids that were homogeneously transgenic for some foreign gene. Researchers were not proven right, however, and they found that the more each gene was expressed, the less editing was occurring at other sites. When comparing the sequences around the introduced sites with sequences around the sites where editing had been altered, the researchers were able to examine discrete transgenic elements that were 5’ of the C target of editing. After seeing this result in the chloroplasts, the researchers suggested that perhaps the same sort of apparatus occurs in the mitochondria, where the same sort of known cis transgenic elements are also able to be observed 5’ of the C target of editing. After conducting an experiment to test this theory, the researchers found that transgenic elements similar to those found on one of the specific sites in the chloroplasts were also found on many mitochondrial genes. Unless there was some feedback mechanism that an increased spread of the factor to the chloroplast sites, it is not likely that the abundance of elements in the chloroplasts affected the editing in the mitochondria.
SOURCE: http://mcb.asm.org/content/22/24/8448.full.pdf+html
ArmstrongGenetics3 
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