It won't force James Watson to retitle the Double Helix, but new research suggests that the three-stranded stretches that frequently turn up in mitochondrial DNA (mtDNA) aren't junk. Instead, the triple-stranded forms might provide a scaffold for a protein that helps mitochondria organize their DNA, as He et al. show on page 141.
Researchers have known for more than 30 years that one section of mtDNA often carries an additional strand, creating a displacement loop, or D-loop. However, the conventional wisdom held that D-loops were nonfunctional leftovers of incomplete replication. He et al. began to doubt that explanation after “we found a protein that is in love with D-loops,” says team leader Ian Holt. Other researchers had previously identified the protein, ATAD3, but knew nothing about its job in mitochondria.
The researchers discovered that ATAD3 prefers to latch onto D-loops, even in solutions...
