MEMBERS OF THE GATA FAMILY OF TRANSCRIPTION FACTORS BIND TO THE U3 REGION OF CAS-BR-E AND GRAFFI RETROVIRUSES AND TRANSACTIVATE THEIR EXPRESSION

Cas-Br-E and Graffi are two murine viruses that induce myeloid leukemi a in mice: while Cas-Br-E induces mostly non-T, non-B leukemia compose d of very immature cells, Graffi causes exclusively a granulocytic leu kemia (E. Rassart, J, Houde, C, Denicourt, M. Ru, C. Barat, E. Edouard , L. Poliquin, and D. Bergeron, Curr. Top. Microbiol, Immunol. 211:201 -210, 1995). In an attempt to understand the basis of the myeloid spec ificity of these two retroviruses, we used DNase I footprinting analys is and gel mobility shift assays to identify a number of protein bindi ng sites within the Cas-Br-E and Graffi U3 regions. Two protected regi ons include potential GATA binding sites. Methylation interference ana lysis with different hematopoietic nuclear extracts showed the importa nce of the G residues in these GATA sites, and supershift assays clear ly identified the binding factors as GATA-1, GATA-2, and GATA-3. Trans ient assays with long terminal repeat (LTR)chloramphenicol acetyltrans ferase constructs showed that these three GATA family members are inde ed able to transactivate Cas-Br-E and Graffi LTRs. Thus, the availabil ity and relative abundance of the various members of the GATA family o f transcription factors in a given cell type could influence the trans criptional tissue specificity of murine leukemia viruses and hence the ir disease specificity.