Transcribes RNA into DNA. Occurs commonly in a lot of ProKaryotes, who sometimes use it to act as vectors for the transmission of genes between otherwise unrelated organisms. This is called HorizontalGeneTransfer, one of the risks of GM foods.

	* http://www.bimcore.emory.edu/home/Kins/CHEM441/Gabe/rt/text.html
		* describes what RT is
	* http://scope.educ.washington.edu/gmfood/controversy/geneTransfer.php
		* talks about deliberate "horizontal gene transfer" through techniques of MolecularBiology
	* http://www.twnside.org.sg/title/let2000-cn.htm
		* a list of people opposed to "horizontal gene transfer" through techniques of MolecularBiology

Still waiting for a list of prokaryotes that have reverse transcriptase and a reference that says these prokaryotes (if they exist) can act as agents of horizontal gene transfer between unrelated organisms.

While on the topic of reverse transcriptase, it should be noted that telomerase, the enzyme that protects the ends of linear chromosomes from degradation, is a reverse transcriptase. To my knowledge, there aren't any examples of an infectious agent transferring genes from one organism to another, other than the well-studied retroviruses, such as HIV, that transfer the genomes of the infectious agent itself into the chromosomes of the host. In these cases, however, the transfer is into somatic cells and is not heritable between generations. The above described horizontal gene transfer is definitely one of the ''fears'' of genetically modified foods, but is unlikely to be one of the actual risks. The biggest danger with genetically modified foods, in my opinion, is the tendency to grow these crops to the exclusion of all others, resulting in widespread monoculture with attendant reduction in biodiversity. This is essentially a fait accompli in soybeans. -- AndyPierce

For a (slightly aged) review on bacterial reverse transcriptases (which I have not actually read), see:

"msDNA and bacterial reverse transcriptase" M. Inouye & S. Inouye; Annu Rev Microbiol 45, 163 (1995)

Dr Inouye's web page talks about a deeply strange branched DNA-RNA hybrid structure called msDNA, and the involvement of RT with that:

http://www2.umdnj.edu/bchemweb/HTML/sumiko.html BrokenLink 20050402

-- TomAnderson

''Re "ends of linear chromosomes", are there any non-linear chromosomes which nevertheless have ends?''
Heh. Point taken. I suppose the rolling circle intermediates of some of the bacteriophages (a linear end coming off of a circle) might count as such. There are also some genomes such as lambda phage that are linear, but have the capacity to stick the ends together non-covalently to form a circle.
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CategoryBiology