FIG. 1.

Construction of the recombinant retrovirus MoFe2-MuLV. To construct MoFe2-MuLV, the U3 region of Mo-MuLV was replaced by U3 sequences from the LTR of FeLV-945 (1) between the homologous EcoRV and SmaI sites. (A) Nucleotide sequence and protein binding sites identified in the enhancers found in the U3 region of Mo-MuLV (39) and FeLV (21) LTRs. (B) Diagrammatic representation of the proviral DNAs of Mo-MuLV, FeLV-945, and MoFe2-MuLV, indicating the number of enhancer repeats (open boxes), the 21-bp sequence triplication in the LTR of FeLV-945, and the EcoRV and SmaI sites used to construct the recombinant. (C) Nucleotide sequence of a segment of the LTR of MoFe2-MuLV, indicating a single copy of the transcriptional enhancer with predicted nuclear protein binding sites (LVa, LVb, core, NF-1, and GRE [21]), followed by a 21-bp sequence repeated three times in tandem (indicated by the brackets and numbers). CCAAT and TATA boxes in the promoter (double underline), the positions of PCR primers used for amplification as described in the text (MoFeA and MoFeB), and the EcoRV and SmaI sites that represent the junctions between MuLV- and FeLV-derived sequences are also indicated.