ATLANTA - Mariner transposable elements, more popularly known as jumping genes, appear to jump from species to species, not randomly but as a fundamental means of survival, reported University of Illinois researchers at the annual meeting of the American Association for the Advancement of Science.

Transposable elements are fragments of DNA which appear to migrate from species to species by an as yet little understood mechanism through a process known as horizontal transfer. Mariner elements, which have been identified in many different species of insects are among the smallest of the jumping genes so far identified.

Mariner transposable element were first identified in Drosophila maurintiana, a fly native to the Indian Ocean region. University of Illinois entomologist Hugh Robertson has identified other mariner elements in more than 400 arthropod species. One of the most unusual discoveries was a jump of a mariner element between an African malaria-vector mosquito and a green lacewing, which are members of two different orders of insects.

The mariner element is a DNA sequence about 1,300 base pairs long. It is characterized by short inverted terminal repeat sequences with a single gene between them. Robertson believes that gene encodes a single protein that binds the inverted terminal repeats and then physically moves the element as a DNA molecule. The mariner elements cannot jump without this enzyme, he says.

Robertson uses many molecular biology techniques in his work including (polymerase chain reaction) and DNA cloning. His most recent studies indicate that only two base pairs of the 1,044 total pairs were different in the central gene of the mariners in the mosquito and the lacewing.

"We've begun to realize that the evolutionary patterns of the elements made no sense in terms of the evolutionary history of the hosts, implying they are jumping around, that there are horizontal transfers occurring." It has become more and more clear that many jumps have occurred in recent evolutionary time," Robertson said in an interview.

While it is now clear that these DNA fragments migrate across species, the method by which they do this remains a mystery. One hypothesis is that environmental factors are responsible, such as mites carrying blood from one creature to another, or that random DNA molecules are picked up as part of everyday life.

"Our impression from our data is that the evolutionary fate of these transposable elements within any particular host is that they eventually will die by mutation and become non-functional. By jumping to a new host, they get a new lease on life before dying out in the old host. Horizontal transfer perhaps explains both the persistence of these elements in evolutionary time and the diversity of hosts that they are found in. Practically every time we find a transposable element in a particular species, the closest relative of the transposable element will be found in a completely unrelated insect," noted Robertson.

A better understanding of transposable elements could have ramifications not only for entomology but for genetic engineering as well, says Robertson:

"There is a practical importance in that we hope to find an isolate, active versions of these elements, in all sorts of different insects, particularly those with economic and medical importance. For basic research, we want to find out how genes work. One of the major interests in entomology is to develop transposable elements such as mariners as tools that can be used to modify other insects. We want to be able to genetically manipulate mosquitoes, beetles, moths and mites, for example, for both agricultural and medical interests."

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