THE PU.1 SPI-1 PROTOONCOGENE IS A TRANSCRIPTIONAL REGULATOR OF A LENTIVIRUS PROMOTER/

The enhancer unit present in the retrovirus equine infectious anemia v irus (EIAV) was previously shown to contain binding sites for proteins belonging to MDBP, PEA2, AP-1, and ets families. The EIAV ets motif m atches the consensus sequence for both PEA3- and PU.1-binding sites. H ere, we show by gel shift analysis that PU.1, present in nuclear extra cts from monocyte and B-lymphocyte cell lines, binds to oligonucleotid es containing the EIAV ets element. HeLa cells transiently transfected with a PU. 1 expression plasmid expressed nuclear factors that formed complexes indistinguishable from those seen with monocyte extracts. A ntibodies to PU.1 protein either supershifted or abolished formation o f these complexes, depending on the PU.1 epitopes recognized. The bind ing of PU.1 to the EIAV ets motif in vitro correlated with transcripti onal activity of the EIAV promoter in transfected monocyte cell lines. In HeLa cells, the product of PU.1 cDNA bound to the EIAV ets motif a nd activated transcription from the EIAV promoter. The PU.1-binding si te was the primary determinant of EIAV promoter activity in cell lines that express PU.1. Nucleotide determinants of PU.1 binding and a cons ensus PU.1 binding sequence were defined in gel shift assays using a p anel of mutated oligonucleotides. To our knowledge, this is the first report of a retroviral promoter controlled by PU.1.