Surprisingly it was neither identical to MuLV nor to the novel xenotropic MuLV related retrovirus (XMRV) but showed 99% identity to a synthetic retrovirus which was engineered in the 1980s.
full text http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2760500/?tool=pubmed
... we found 12 sequences in the RNA preparation that showed high similarity scores (97-100%) to five different regions within either the gag and pol gene or the LTR region of squirrel monkey retrovirus (SMRV, Fig. Fig.2A)2AFigure 2) by analyses on nucleotide level. Additionally we isolated seven clones that bore six different sequences with high similarity scores of 97-100% to murine leukemia virus strains (MuLV) in a nucleotide BLAST search. These sequences were located within the LTR and the gag, pol and env genes...
... The resulting sequence of the simian retrovirus (7.968 kbp) confirmed our preliminary identification as squirrel monkey retrovirus [GenBank: M23385.1] with an overall sequence identity of 98,5%. In contrast the 7.4 kbp sequence of the murine retrovirus was neither identical to one of the murine leukemia viruses nor to XMLV but showed an overall similarity score of 99% to pAMS [GenBank: AF010170], a plasmid carrying the proviral sequence of a recombinant hybrid virus. This construct was engineered in the 1980s and is composed of sequences from Moloney murine leukemia virus (MoMLV) and amphotropic mouse leukemia virus clone 4070A [7,8]. In the current GenBank entry it is described as "... reference retrovirus for FDA validation of retrovirus vectors used for human gene therapy...". Neither the hybrid virus itself nor the plasmid pAMS were ever used in our laboratory. Due to the high identity of nucleotide sequence and the fact that the structure of MoMLV and amphotropic leukemia virus related segments is 100% identical to that of pAMS (data not shown) we can exclude that the contaminant virus is a natural recombinant of MoMLV and amphotropic leukemia virus.
.... t has to be mentioned that each of both viruses was found in at least one aliquot of all cell lines tested. Thus, we cannot report a single cell line which is not permissive for one of both viruses. Furthermore, experimental infections of retrovirus-negative aliquots of selected cell lines showed that both viruses are highly infectious and propagate to high viral loads...
... In summary, there have been numerous publications about retroviral contaminations like recent reports of ecotropic murine leukemia virus in various cell lines [11,12]. The most frequent retrovirus found in this context is squirrel monkey retrovirus (SMRV) [13-16]. One study even reported the detection of SMRV related sequences in commercial interferon preparations in 1998 [17]. Although the sequences were found only as DNA and therefore rather derived from cellular DNA carrying proviral genomes than viral particles, it clearly demonstrated the contamination of the interferon producing cell line with SMRV. Germany's Central Commission of Biosafety (ZKBS) recently reported that SMRV was detectable in 128 samples of 4279 cell cultures from different laboratories throughout the country [18].
The present report extents these studies by identifying for the first time a presumably synthetic chimeric retrovirus as a contaminant. This gene-modified organism seems to have replicated and spread intensely in a broad set of cell lines for several years without being noticed. This hybrid amphotropic/Moloney murine leukemia virus was engineered in the 1980s [7,8] and neither the virus itself nor the plasmid (pAMS) containing its proviral genome were ever used in our laboratory. Although the precise source for the contamination could not be traced back, sharing cell lines with other laboratories seems the most likely explanation....
full text http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2760500/?tool=pubmed
... we found 12 sequences in the RNA preparation that showed high similarity scores (97-100%) to five different regions within either the gag and pol gene or the LTR region of squirrel monkey retrovirus (SMRV, Fig. Fig.2A)2AFigure 2) by analyses on nucleotide level. Additionally we isolated seven clones that bore six different sequences with high similarity scores of 97-100% to murine leukemia virus strains (MuLV) in a nucleotide BLAST search. These sequences were located within the LTR and the gag, pol and env genes...
... The resulting sequence of the simian retrovirus (7.968 kbp) confirmed our preliminary identification as squirrel monkey retrovirus [GenBank: M23385.1] with an overall sequence identity of 98,5%. In contrast the 7.4 kbp sequence of the murine retrovirus was neither identical to one of the murine leukemia viruses nor to XMLV but showed an overall similarity score of 99% to pAMS [GenBank: AF010170], a plasmid carrying the proviral sequence of a recombinant hybrid virus. This construct was engineered in the 1980s and is composed of sequences from Moloney murine leukemia virus (MoMLV) and amphotropic mouse leukemia virus clone 4070A [7,8]. In the current GenBank entry it is described as "... reference retrovirus for FDA validation of retrovirus vectors used for human gene therapy...". Neither the hybrid virus itself nor the plasmid pAMS were ever used in our laboratory. Due to the high identity of nucleotide sequence and the fact that the structure of MoMLV and amphotropic leukemia virus related segments is 100% identical to that of pAMS (data not shown) we can exclude that the contaminant virus is a natural recombinant of MoMLV and amphotropic leukemia virus.
.... t has to be mentioned that each of both viruses was found in at least one aliquot of all cell lines tested. Thus, we cannot report a single cell line which is not permissive for one of both viruses. Furthermore, experimental infections of retrovirus-negative aliquots of selected cell lines showed that both viruses are highly infectious and propagate to high viral loads...
... In summary, there have been numerous publications about retroviral contaminations like recent reports of ecotropic murine leukemia virus in various cell lines [11,12]. The most frequent retrovirus found in this context is squirrel monkey retrovirus (SMRV) [13-16]. One study even reported the detection of SMRV related sequences in commercial interferon preparations in 1998 [17]. Although the sequences were found only as DNA and therefore rather derived from cellular DNA carrying proviral genomes than viral particles, it clearly demonstrated the contamination of the interferon producing cell line with SMRV. Germany's Central Commission of Biosafety (ZKBS) recently reported that SMRV was detectable in 128 samples of 4279 cell cultures from different laboratories throughout the country [18].
The present report extents these studies by identifying for the first time a presumably synthetic chimeric retrovirus as a contaminant. This gene-modified organism seems to have replicated and spread intensely in a broad set of cell lines for several years without being noticed. This hybrid amphotropic/Moloney murine leukemia virus was engineered in the 1980s [7,8] and neither the virus itself nor the plasmid (pAMS) containing its proviral genome were ever used in our laboratory. Although the precise source for the contamination could not be traced back, sharing cell lines with other laboratories seems the most likely explanation....