Expression of a human beta-globin transgene in mice with the CACC motif and upstream sequences deleted from the promoter still depends on erythroid Kruppel-like factor

Mice in which the erythroid Kruppel-like Factor (EKLF) gene is inactivated die in fetal life due to downregulation of the beta-globin gene. Results ha ve suggested that EKLF functions through the proximal CACC motif of the bet a-globin promoter. For example, natural mutations of this element that fail to bind EKLF give reduced gene expression and the ability of EKLF to activ ate reporter genes in co-transfection assays is dependent on an intact CACC , Here, removal of the CACC motif and upstream promoter sequences from the beta-globin gene resulted in reduced expression in transgenic mice. However , breeding onto an EKLF-/- background demonstrated that a CACC-less beta-gl obin transgene remains highly dependent on EKLF. Hence, although the beta-g lobin gene partly depends on the proximal CACC motif for expression, it is unlikely that the major mechanism of gene activation by EKLF is through thi s element. We also show that a lacZ reporter gene linked to the beta-globin promoter, with or without the CACC box present, is actually expressed high er in EKLF-/- fetuses than in wild type animals, suggesting that EKLF may b e able to act as an inhibitor of transcription with certain transgene confi gurations.