A single mutation in one of the core elements of moloney murine leukemia virus reduced binding of a 42‐kDa T lymphoma cell nuclear factor but did not affect lymphomagenesis

The genetic determinant responsible for virulence in Moloney murine leukemia virus (MoMuLV) induced T‐cell lymphomagenesis has recently been mapped [J Virol 63:471–480, 1989] by homologous genomic fragment exchange between MoMuLV and MoMuLV‐TB to the Clal/Xbal at the 3' end of the genome. This region of MoMuLV and MoMuLV‐TB differs in 11 nucleotides. Of these 11 nucleotide differences, 9 are distributed within the two CORE, the two distal NF1, and the two GRE/LVa elements of the enhancer. Since both the CORE binding sites of MoMuLV‐TB are mutated with respect to those of MoMuLV, we compared nuclear proteins of a thymusbone marrow cell line and a T‐lymphoma cell line (EMT), which bind to the wild‐type and mutant CORE binding sites. Using both the bandshift assay and southwestern analysis with labeled synthetic deoxyoligonucleotides, we showed that a 42‐kDa protein from TB and EMT cells bound specifically to the MoMuLV CORE element. The T SSC transversion of nucleotide 6 of the CORE consensus, TGTGGT/CTAA, significantly reduced binding of the 42‐kDa TB and EMT cell factors. However, the transversion of nucleotide 3 from T →C had little effect on the binding of the 42‐kDa protein to the CORE element. In addition, the 42‐kDa protein bound weakly to the CCAAT element of MoMuLV. A recombinant virus, NwtTB‐6, was generated by introducing the two CORE mutations of MoMuLV‐TB into the MoMuLV genome. Although the latency period of NwtTB‐6 in the induction of lymphoma was not significantly different from that of MoMuLV, preliminary findings suggest that the lymphoma induced by NwtTB‐6 may be more widely distributed.