The xenotropic murine leukemia virus-related virus (XMRV) has been implicated as a possible causative agent of prostate cancer and chronic fatigue syndrome (CFS). Scientists at the National Institutes of Health (NIH) and Science Applications International Corporation in Frederick, MD (SAIC-Frederick) have developed sixty four (64) protein expression plasmids for components of XMRV. One or more XMRV proteins made available through these expression plasmids could have clinical relevance to diagnosing or treating human disease. The work to develop this technology was performed in the Protein Expression Laboratory at SAIC-Frederick in collaboration with expert retrovirologists from the National Cancer Institutes Frederick, MD campus, a site well-positioned to develop these expression plasmids from initial cloning to final validations. The development of these XMRV tools is expected to save researchers months in laboratory production time and thousands of dollars in labor costs. The XMRV strain utilized to generate these expression plasmids is a reference strain isolated from a human patient. Each expression plasmid encodes one of the ten proteins that comprise the XMRV retrovirus (matrix, p12, capsid, nucleocapsid, protease, reverse transcriptase, integrase, surface, transmembrane, and envelope). Nine of the ten XMRV proteins expressed by these clones have been successfully purified in large quantities using scale-up processes. The expression vectors were generated utilizing the Gateway? cloning system and consist of Gateway? entry clones, bacterial (Escherichia coli) expression clones, baculovirus expression clones, and mammalian expression clones. Expression of the appropriate XMRV protein from its corresponding expression clone has been confirmed. The entry clones have been validated for Gateway? subcloning and the baculovirus clones have been validated for baculovirus production and can be transposed into baculoviral genomes. The plasmids have been fully mapped and sequenced and contain one or more elements to facilitate laboratory use, such as antibiotic resistance genes, specialized promoter sequences, maltose-binding protein and His tags, TEV protease sites, Kozak-ATG sequences, signal peptides, and other elements.