Conducted by scientists from the University of Michigan Medical School and Louisiana State University, the study is the first to show in mammalian cells that some human LINE-1, or L1, elements can jump to chromosomes with broken strands of DNA, slip into the break and repair the damage.
Transposable L1 elements make up 17 percent of our DNA, but very little is known about them, says John V. Moran, Ph.D., an assistant professor of human genetics and internal medicine in the U-M Medical School, who developed the first assay to identify mobile L1s in the human and mouse genomes. Until now, everyone thought L1s were just intracellular parasites in our DNA leftovers from the distant evolutionary past. The big question in the field is: Are they still there because we cant get rid of them or do they have a function?
L1s reproduce by using RNA and a process called reverse transcription to make complementary DNA copies of themselves, which can jump into other DNA sequences. Normally, L1s use an enzyme called endonuclease to cut the genetic DNA and create a space, so they can plug themselves into the genome.
We knew about the endonuclease pathway, says Tammy A. Morrish, a U-M graduate student in human genetics and first author of the paper. But we didnt know there was another mechanism that didnt require endonuclease, or that L1s could jump into existing breaks in DNA.
Morrish tested human L1s ability to repair DNA breaks in several normal and DNA-repair mutant cell lines derived from Chinese hamster ovary cells. Other researchers had demonstrated the ability of human L1s to repair DNA breaks in yea
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Contact: Sally Pobojewski
pobo@umich.edu
734-615-6912
University of Michigan Health System
12-May-2002