Characterization of nuclear protein binding to a site in the long terminal repeat of a murine leukemia virus: comparison with the NFAT complex.
We previously identified a protein-binding site (MLPal) that is located downstream of the enhancer element in the long terminal repeat (LTR) of a mink cell focusing-forming (MCF) murine leukemia virus (F. K. Yoshimura, K. Diem, H. Chen, and J. Tupper, J. Virol. 67:2298-2304, 1993). We determined that the MLPal site regulates transcription specifically in T cells and affects the lymphomagenicity of the MCF isolate 13 murine leukemia virus with a single enhancer repeat in its LTR. In this report, we present evidence that two different proteins, a T-cell-specific protein and a ubiquitous protein, bind the MLPal site in a sequence-specific manner. By mutational analysis, we determined that the T-cell-specific and the ubiquitous proteins require different nucleotides in the MLPal sequence for DNA binding. By competitive electrophoretic mobility shift assays, we demonstrated that the T-cell-specific protein that binds MLPal is identical or similar to a protein from nonactivable T cells that interacts with the binding site of the nuclear factor of activated T cells (NFAT). Unlike the NFAT-binding site, however, the MLPal site does not bind proteins that are inducible by T-cell activation. We observed that the MLPal sequence is conserved in the LTRs of other mammalian retroviruses that cause T-cell diseases. Furthermore, the MLPal sequence is present in the transcriptional regulatory regions of cellular genes that either are expressed specifically in T cells or are commonly rearranged by provirus integration in thymic lymphomas. Thus, the MLPal-binding proteins may play a role in the transcriptional regulation not only of the MCF virus LTR but also of cellular genes involved in T-cell development.
Yoshimura
F K
FK
Department of Biological Structure, University of Washington, Seattle, Washington 98195.
Diem
K
K
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002352:Carrier Proteins / Q000502:physiology; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005809:Genes, Regulator; D051379:Mice; D008908:Mink Cell Focus-Inducing Viruses / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins / Q000378:metabolism*; D012091:Repetitive Sequences, Nucleic Acid; D014157:Transcription Factors / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D050778:NFATC Transcription Factors; D009687:Nuclear Proteins; D014157:Transcription Factors