GATA-3 is essential for murine embryonic development, but elucidating the genetic controls over the complex temporal and tissue-specific transcriptional regulatory pattern of this transcription factor gene has been problematic. Here we report the isolation and characterization of two yeast artificial chromosomes (YACs) bearing the murine GATA-3 gene. Ordered deletions of both YACs show that they define a 1-megabase pair contig spanning the GATA-3 locus. We found that a 120-kb YAC transgene, including 35 kb of 5′ as well as 60 kb of 3′ flanking sequence, confers normal GATA-3 expression at sites not revealed previously through analysis of plasmid transgenic lines. However, even this 120-kb YAC does not contain sufficient information to recapitulate the complete GATA-3 expression program during embryogenesis. While not complete in its regulatory capacity, the YAC transgene is nonetheless able to complement several homozygous GATA-3 mutant phenotypes and thereby prolong embryonic life.