FRIDAY, March 21 (HealthDay News) -- Cockayne syndrome, an especially severe type of progeria often caused by mutations in the CSB gene, may be linked to a fusion protein that dates back in primates at least 43 million years, according to research published online March 21 in PLoS Genetics.
John C. Newman, of the University of Washington in Seattle, and colleagues write that the so-called PiggyBac transposable element PGBD3 is embedded within intron 5 of the CSB gene, so that the CSB locus encodes two proteins in equal abundance: the original CSB protein, and a CSB-PiggyBac fusion protein. This fusion protein has been highly conserved since humans and marmosets diverged.
The authors speculate that the fusion protein is usually beneficial. Since CSB mutations that cause Cockayne syndrome usually still produce the fusion protein -- and a mutation that interferes with both proteins doesn't cause the syndrome -- the fusion protein may act in helpful or harmful ways, depending on the presence of working CSB.
"We speculate that the CSB-transposase fusion protein originally played a role in host genome defense by repressing transposition of autonomous PGBD3 elements and the hundreds of nonautonomous PGBD3-dependent MER85 elements derived from them," the authors write. "We do not yet know why the CSB-PGBD3 fusion protein has been selected and maintained in the primate lineage for over 43 million years, but the answers will undoubtedly shed light on both CSB function and the longevity of PiggyBac transposases from cabbage looper moths to humans."
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