CHARACTERIZATION OF A CIS-ACTING SEQUENCE IN THE POL REGION REQUIRED TO TRANSFER HUMAN FOAMY VIRUS VECTORS

To identify cia-acting elements in the foamy virus (FV) RNA pregenome, me developed a transient-vector-production system based on cotransfec tion of indicator gene-bearing vector and gag-pol and env expression p lasmids. Two elements which were critical for vector transfer were fou nd and mapped approximately. The first element was located in the RU5 leader and the 5' gag region (approximately up to position 650 of the viral RNA). The second element was located in an approximately 2-kb se quence in the 3' pol region. Although small 5' and 3' deletions, as we ll as internal deletions of the latter element, were tolerated, both e lements were found to be absolutely required far vector transfer. The functional characterization of the pol region-located cia-acting eleme nt revealed that it is essential for efficient incorporation or the st ability of particle-associated virion RNA. Furthermore, virions derive d from a vector lacking this sequence were found to be deficient in th e cleavage of the Gag protein by the Pol precursor protease. Our resul ts suggest that during the formation of infectious virions, complex in teractions between FV Gag and Pol and the viral RNA take place.