The targeting contruct introduced downstream of exon 1 a floxed STOP and neomycin resistance cassette, three hemagglutinin (HA) tags, a truncated Vav2 cDNA (delta1-184) and a human growth hormone polyadenylation sequence. This truncated version is a phosphorylation-independent and has constitutitive exchange activity due to the removal of the N-terminal inhibitory domains. (J:224320)