The Mos1 gene carries the code to make an enzyme named Mos1 transposase. That enzyme does the actual cutting of DNA, Frkjr-Jensen says.
The transposons in the new study came from fruit flies and were placed into the worm genetic blueprint by French scientists who provided them to the Utah team.
Frkjr-Jensen says the Utah researchers crippled the jumping genes put into worms "so we can control when and where they hop."
The Utah biologists used a plasmid a circular piece of DNA as a carrier by injecting it with the gene for Mos1 transposase, the "scissors" that cut DNA. Then, a glass needle was used to inject the combination into a worm's gonad.
The transposase-carrying plasmid then cuts out a Mos1 jumping gene adjacent to a gene that researchers want to knock out, leaving a break in the chromosome's DNA.
Cell machinery kicks in to repair the DNA break. Since chromosomes come in pairs, the repair process normally uses the undamaged twin chromosome as a template for repairing the break. But "in this case, we flood the cell with DNA that's similar to where the DNA was broken," Frkjr-Jensen says. "We essentially trick the DNA machinery into repairing off a template we supply."
But the template provided by the biologists lacks the DNA for the gene they want to delete. Thus, the gene is knocked out in the worm's offspring.
DNA is made of "bases" known as G, A, T and C. By "repairing" the broken chromosome, the new method can delete up to 25,000 pairs of those bases. Typical worm genes are 5,000 bases, but range from 700 bases to 30,000 bases.
Frkjr-Jensen says that to determine how long a segment of worm DNA could be targeted for deletion, the researchers designed repair templates ranging from 1,000 to 50,000 base pairs. They found their method could knock out a gene reliably only if that gene was within 25,000 base
|Contact: Lee Siegel|
University of Utah