Mechanisms of transcription in eosinophils: GATA-1, but not GATA-2, transactivates the promoter of the eosinophil granule major basic protein

Granule major basic protein (MBP) is expressed exclusively in eosinophils, basophils, and placental trophoblasts. To identify the cis-elements and transcription factors involved in regulating MBP expression, we subcloned 3.2 kb of sequence upstream of the exon 9 transcriptional start site (P2 promoter) and serial 58 deletions into the pXP2 luciferase reporter vector. An 80 % decrement in promoter activity was obtained when MBP sequences between bp 2117 to 267 were deleted. To identify transcription factors that bind to and transactivate through the bp 2117 to 267 region, we first compared the upstream genomic sequences of human and murine MBP; a potential GATA binding consensus site was conserved in the 50-bp region between the two genes. To determine which GATA proteins bind this consensus site, we performed electrophoretic mobility shift assays (EMSAs), which showed that both GATA-1 and GATA-2 can bind to this consensus site. To determine the functionality of this site