Approximately 70kb genomic fragment (BAC clone CH321-28E21) that encompasses the vri locus (includes approximately 41kb upstream and 3kb downstream sequence relative to the transcription unit). Two FRT sites have been inserted, flanking either side of exon 3 (which contains the bZIP domain). The presence of this FRT cassette allows for conditional inactivation of the rescuing transgene using FLP recombinase.