Role of e boxes in the β-globin locus control region

Regulated expression of the β-globin gene cluster requires the combined action oi the proximal e, y, 6, and β-globin gene promoters and the distal Locus Control Region (I.CR). The I.CR contains 5 DNAse 1 hypersensitive sites (IIS1 -5) located 6-22 kh upstream of the t:-globin gene. A sub-fragment of'HS2 capable of conferring the properties of domain opening and enhancement contains API/NFE-2. CACCC, and GATA-1 binding sites, as well as conserved sequence blocks that \vc identified through phylogenetic footprinting. Two of these blocks are K box hexamers (CAGATCi) that bind basic helix-loop-helix (bHLH) proleins. We find that the E boxes contribute to the enhancement of globin gene expression by HS2. Furthermore, we show that TAL1/SCL. a bHLH protein required for all hematopoietic lineages; USF; and other proteins bind specifically to these sites. Currently, we are studying the effect of post-translalional modification on the function ot these K box binding proteins.