Expression of vav-βgal transgenes in primary transgenic animals. For the indicated reporter constructs, the proportion of primary animals that showed any β-gal⁺cells in the blood is given. The constructs analyzed were those used in the stable transfection experiments (see Fig 4), plus others containing an additional intronic hypersensitive site (HS4), also placed 3′ of the polyadenylation site in the reporter gene.