Genome complexity: fighting retrotranspositions (Introduction)

by David Turell , Sunday, April 27, 2014, 16:02 (3864 days ago) @ David Turell

Some DNA plays a rogue process, contaminating DNA with bad mutations. There is a defense mechanism:-"In addition to fighting LINE-1 jumps that can cause mutations, APOBEC enzymes also fight off certain viruses. In fact, scientists first discovered these enzymes when observing how human cells fight off infection by HIV, the virus that causes AIDS.
 
:Just like HIV, LINE-1 spreads throughout our DNA by making an RNA copy of its genetic sequence. Then, the RNA is copied back into a new LINE 1 copy that can slide into a new location in our DNA -- a process called retrotransposition.
 
"In this new paper, the researchers show that LINE-1 has one important point of vulnerability. When the new DNA copy peels away from the RNA, an APOBEC3A molecule can attach and change some of the "letters" or base-pairs (rungs on the DNA ladder) in the DNA sequence. Specifically, it changes the "C" bases to "U" bases. The presence of those U bases triggers the cell's cleanup mechanism to come in and dismantle the new copy of the rogue DNA.
 
"In other words, APOBEC3A preempts a potential mutation by LINE-1 jumping, by itself causing a mutation in the new LINE-1 copy that the cell then destroys. But APOBEC3A can pose a mutation danger to the rest of our DNA -- which means our cells must strike a balance between a vigorous defense and the danger of friendly fire.
 
"This kind of intracellular "immunity" may have been raging since the beginnings of life on earth, Moran speculates. LINE-1 contains the code for a molecule called reverse transcriptase -- the kind of molecule that would have been crucial when higher life forms started to evolve and use DNA instead of the less stable RNA to carry genetic information." (Love these speculations!)-
http://www.sciencedaily.com/releases/2014/04/140425091846.htm