To detect viruses from tissue samples, the researchers isolated genetic material from each sample and tagged the genetic material with a fluorescent tracer. They then applied the fluorescently tagged genetic material to the microarray chip. Since genes tended to adhere to those with a complementary genetic sequence, any viral gene sequences in the sample would attach themselves to corresponding viral sequences on the chip. The telltale fluorescence on spots on the chip signaled the presence of viral genetic material in the sample.
Although the Virochip contains only sequences from known viruses, DeRisi said it can also detect new viruses because they invariably contain sequences that have been conserved in their evolution from related viruses.
The initial screen of the RNASEL-mutant prostate cancers revealed the presence of a genetic sequence that closely resembled that of a mouse virus called murine leukemia virus (MuLV). Murine leukemia virus is known as an endogenous virus because it normally exists as an integrated part of the mouse genome, rather than as independent, infective particle. MuLV is also a retrovirus, meaning its genetic material is in the form of RNA. The RNA is then reverse transcribed into DNA that is integrated into the DNA of the host cell the virus is infecting.
When the researchers isolated and sequenced the genome of the virus, they found that it was a xenotropic virus one that can only grow in foreign cells other than mouse cells. Thus, they named the virus, Xenotropic MuLV-related virus, or XMRV.
"This finding was a big surprise because most of these endogenous viral genomes have undergone such mutation and de
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Contact: Jim Keeley
keeleyj@hhmi.org
301-215-8858
Howard Hughes Medical Institute
30-Mar-2006