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

Mice in which the erythroid Krüppel-like Factor (EKLF) gene is inactivated die in fetal life due to down-regulation of the beta-globin gene. Results have suggested that EKLF functions through the proximal CACC motif of the beta-globin promoter. For example, natural mutations of this element that fail to bind EKLF give reduced gene expression and the ability of EKLF to activate 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-globin transgene remains highly dependent on EKLF. Hence, although the beta-globin gene partly depends on the proximal CACC motif for expression, it is unlikely that the major mechanism of gene activation by EKLF is through this 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 higher in EKLF-/- fetuses than in wild type animals, suggesting that EKLF may be able to act as an inhibitor of transcription with certain transgene configurations.