The transgene construct comprises sequence containing the mouse Gata1 hematopoietic regulatory domain (G1-HRD) (3.9 kb sequence 5' of the IE exon, the IE exon, intron 1 and part of exon 2; the initiation ATG codon in exon 2 was replaced with a NotI restriction site) upstream of the mouse Runx1 gene. This allele drives the transgene only in hematopoietic tissue. (J:117242)