When the project began, Gilbert and Lutz-Prigge were simply looking for a faster, more efficient way to figure out where L1s land when they jump and what changes L1s make in the original DNA sequence. Instead of using time-consuming, traditional molecular cloning techniques, they developed a new plasmid cassette technology and used E. coli bacteria to churn out multiple copies of DNA at the insertion site.
"Before Nico and Sheila developed this technique, we could jump L1s into cells, but we could never get them out efficiently," Moran explains. "Now we can see where L1s integrate and what they change. Access to the draft human genome lets us isolate the original site prior to L1 integration, and compare it with the post-integration sequence. We have gone from characterizing four events over a six-year period to about 50 events within the last 18 months."
Moran says one of the more intriguing results of the study is that L1s use different mechanisms to create new breaks, or take advantage of existing breaks, in DNA. He suspects L1s interact in multiple ways with host enzymes in the cell.
"The L1 is always the same, no matter what cell it's in, so if you end up with different rearrangements, that implies interaction between host factors and the L1 retrotransposition machinery," he says. "The more we study L1s, the more we realize how little we know about them. In biology, the stories are always simple until somebody delves deeper into them."