Summary. B7 is the designation of a cell clone derived from the human cell line CEMx174, which was infected with SIVsmH3 clone. B7 cells chronically produce high quantities of non-infectious virus-like particles (VLP) denominated SIVsmB7. Here we report the molecular characterization of the B7 cell line. We found that B7 cells have a single copy of the SIVsmB7 provirus integrated in a noncoding region of chromosome 20 (nt 24,957 of clone RP5-963K23 on human chromosome 20q 13.11-13.2). Similarly to HIV and SIVmac, we show that integration of SIVsm results in a characteristic five base pair sequence repeat of host DNA that flanks the proviral DNA genome. Since the SIVsmB7 genome has a deletion in the IN coding sequence, the generation of this defective proviral genome most likely occurred during a faulty process of reverse transcription. Thus, these studies reveal the molecular clonality of the SIVsmB7 VLP produced by B7 cells. These genetically homogeneous VLP are useful reagents for vaccine development. In addition, these particles have been used by others (Montelaro et al.) to study the maturation of immune system responses to SIV infection.
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