Alternative DNA chemistry

http://en.wikipedia.org/wiki/DNA

For a number of years exobiologists have proposed the existence of a shadow biosphere, a postulated microbial biosphere of Earth that uses radically different biochemical and molecular processes than currently known life. One of the proposals was the existence of lifeforms that use arsenic instead of phosphorus in DNA. A report in 2010 of the possibility in the bacterium GFAJ-1, was announced,though the research was disputed,and evidence suggests the bacterium actively prevents the incorporation of arsenic into the DNA backbone and other biomolecules.