antibiotics

‘Jumping genes’ use bacteria to go viral

CORNELL (US)—A small piece of foreign DNA recognizes when and where to slip into a bacterium’s genetic code, allowing bacteria to genetically adapt to their environment—and develop resistance to antibiotics—a team of researchers has found.

The study hones in on sequences of DNA called Tn7, known as transposons, which have the ability to move from place to place. Tn7 contain a cargo area where as many as 50 genes may attach and insert themselves into a host’s genome.

Researchers believe the findings may one day lead to better detection and treatment of cancers.

“Bacteria evolve through the mass transfer of genes,” says senior author Joseph Peters, associate professor of microbiology at Cornell University. “We had no idea Tn7 had such reach that it does. I know of no other genetic element that has the reach of Tn7.”

While researchers have long known that “jumping genes” were involved in antibiotic resistance, the new study explains exactly how Tn7 and related “jumping genes” transfer genetic information in bacteria around the world.

The study also describes why there is reason to believe many transposons use a similar mechanism to introduce new genetic information into life forms, including flies, plants and possibly even humans.

Antibiotic resistance moves from one bacterium to another. The paper describes how in carrying genes that transfer antibiotic resistance, Tn7 recognizes a ring of proteins called processivity factors, which are essential proteins found in all living organisms and are part of the DNA replication machinery in cells.

Processivity factors circle the DNA like a washer around a string and create a sliding platform that controls replication, where the DNA of one cell copies itself to create a new cell.

By recognizing and attaching itself to processivity factors during replication, Tn7 takes advantage of gaps in the host cells’ DNA and inserts itself and its cargo of genetic information, thereby altering the genetic makeup of the new cell. In this way, such traits as antibiotic resistance can transfer efficiently between bacteria.

Because processivity factors are essential to all cells, Tn7 can move between very different types of bacteria.

The scientists believe the new work may help explain why previous studies of processivity factors in other organisms also identified proteins associated with jumping genes, a finding that remained a mystery until now.

“If you look at transposable elements, you find similar protein enzymes that bind to processivity factors in other species,” explains Peters. “Knowing how Tn7 works gives us clues to how genetic information can be transferred between living organisms in different corners of the world.”

Adam Parks, a former graduate student in Peters’ lab and now a postdoctoral fellow at the National Cancer Institute Center for Cancer Research, is the paper’s lead author.

The study, which appears in the journal Cell, was funded by the National Institutes of Health.

Cornell University news: www.news.cornell.edu

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