As retrotransposons arise and start jumping around a host genome, the host develops ways to fend them off, sparking a sort of "evolutionary arms race," as researchers led by University of California, Santa Cruz's David Haussler put it.
Haussler and his colleagues report in Nature that they've uncovered two KRAB zinc-finger protein-encoding genes that have evolved in the human genome to deal with the retrotransposon menace.
ZNF91, they found, went through a number of structural changes about 8 million to 12 million years ago that allowed it to combat the SINE-VNTR-Alu retrotransposons. The other, ZNF93, evolved even earlier to earlier to repress the primate lineage of long interspersed nuclear element 1 retrotransposons. However, the L1PA3-subfamily of retrotransposons has lost its ZNF93-binding site, escaping the reaches of ZNF93.
"The hosts thrusts, the parasite parries, and the duel continues. But unlike more familiar battles between snakes and toads, or hosts and viruses, this is a case where we're waging war against our own DNA," notes Ed Yong at Not Exactly Rocket Science.