The putative oncogene Spi-1: murine chromosomal localization and transcriptional activation in murine acute erythroleukemias

We have shown previously that spleen focus forming virus integration near the Spi-1 putative oncogene is observed in 95% of erythroid Friend tumors (Moreau-Gachelin et al., 1988). Here we describe how the proviral insertion in the Spi-1 domain is associated with the enhanced transcription of a 1.4 kb mRNA normally expressed at a low level in normal cells. The gene is localized on murine chromosome 2, band E3. The structure of the Spi-1 gene was determined by sequencing genomic and cDNA clones. The gene has an open reading frame encoding a protein of 218 amino acids, extending over five exons. Proviruses always integrate outside, upstream and in the opposite orientation of the protein-encoding domain. This suggests that SFFV integration activates the expression of Spi-2 gene that may contribute to the erythroleukemic process.