The Vav gene was originally identified on the basis of its oncogenic activation during the course of gene transfer assays. The major translational product of the Vav proto-oncogene has been identified as a protein containing an array of structural motifs. Contained within its amino terminus are a helix-loop-helix domain and a leucine zipper motif similar to that of Myc family proteins; deletion of this region of p95Vav causes its oncogenic activation. In addition, p95Vav contains an SH2 domain, which could indicate its role as a substrate for tyrosine kinases. Expression of p95Vav is limited exclusively to cells of hematopoietic origin, including those of the erythroid, lymphoid and myeloid lineages.