Evi9 encodes a novel zinc finger protein that physically interacts with BCL6, a known human B-Cell proto-oncogene product

Evi9 is a common site of retroviral integration in BXH2 murine myeloid leuk emias. Here we show that Evi9 encodes a novel zinc finger protein with thre e tissue-specific isoform;: Evi9a (773 amino acids [aa]) contains two C2H2- type zinc finger motifs, a proline-rich region, and an acidic domain; Evi9b (486 aa) lacks the first zinc finger motif and part of the proline-rich re gion; Evi9c (239 aa) lacks all but the first zinc linger motif, Proviral in tegration sites are located in the first intron of the gene and lead to inc reased gene expression. Evi9a and Evi9c, but not Evi9b? show transforming a ctivity for NIH 3T3 cells, suggesting that Evi9 is a dominantly acting prot o-oncogene, Immunolocalization studies show that Evi9c is restricted to the cytoplasm whereas Evi9a and Evi9b are located in the nucleus, where they f orm a speckled localization pattern identical to that observed for BCL6, a human B-cell proto-oncogene product, Coimmunoprecipitation and glutathione S-transferase pull-down experiments show that Evi9a and Evi9b, but not Evi9 c, physically interact with BCL6, while deletion mutagenesis localized the interaction domains in or near the second zinc finger and POZ domains of Ev i9 and BCL6, respectively, These results suggest that Evi9 is a leukemia di sease gene that functions, in part, through its interaction with BCL6.