TRANSMISSION AND PROPAGATION IN CELL-CULTURE OF VIRUS PRODUCED BY CELLS TRANSFECTED WITH AN INFECTIOUS MOLECULAR CLONE OF BOVINE LEUKEMIA-VIRUS

A full-length molecular clone of bovine leukemia virus (BLV) pBLV-IF w ith two copies of a long terminal repeat (LTR) was constructed from a previously isolated, covalently closed, circular DNA clone, pB6490, th at has one copy of the LTR and the pX region split at an EcoRI site. T his molecular clone directed the synthesis of viral proteins and the i nduction of syncytia in transiently transfected cells. In addition, vi rus particles were released into the culture medium. Serial passages o f transient transfectants also resulted in propagation of BLV. After t ransfection of five cell lines with linearized pBLV-IF and a neomycin- resistance gene, BLV-producing transfectants were established in cell lines COS-1 and 23CLN that did not form syncytia upon expression of BL V. In HeLa and FLK cells, BLV produced by a stable COS-1 transfectant was transmitted by both cell-free and cell-to-cell infection. Thus, pB LV-IF encoded an infectious provirus that successfully induced primary and secondary infections. This study indicates that the infectious mo lecular clone and the virus-producing transfectants could be useful fo r further examination of the biological properties of BLV. (C) 1998 Ac ademic Press.