Structural and functional analysis of the promoter of the murine Vγ1.1 T cell receptor gene

The expression of the germ‐line gene Vγ1.1‐Cγ4 of the T cell receptor (TcR) γ chain depends on interleukin (IL)‐3 induction in hematopoietic cells, while in T cells, the rearranged gene is expressed constitutively. To understand the mechanism that controls TcRγ gene expression, we cloned and characterized the structure and function of the Vγ1.1‐Cγ4TcR promoter. IL‐3‐dependent cell lines and T cell lines utilized the same transcriptional start sites. In chloramphenicol acetyltransferase (CAT) assays, the minimal 70‐bp promoter confers strong transcriptional activity which is 50–60% of the Moloney long terminal repeat promoter activity. The 500‐bp promoter region linked to the CAT gene exhibits IL‐3 dependency similar to the endogenous TcRγ gene. The immediate 3′ and 5′ flanking sequences inhibit the promoter activity two‐ to fourfold. The promoter lacks an obvious TATA box or CAAT box sequences, but contains a GC box in the untranslated region 3′ to the promoter. The GC box is the core sequence of the element which binds Sp1‐like proteins. Cloning of this Sp1 binding element in front of the thymidine kinase (TK) promoter and mutations generated in this site demonstrate its function as a silencer. Ultraviolet cross‐linking analysis with the Sp1 binding site from the TcRγ promoter revealed binding of a 90–100‐kDa protein in a T cell line (EL‐4) and 40–50 and 90–100‐kDa proteins in FDC‐P1 cells. The possible function of the Sp1‐like protein in silencing the minimal promoter activity is discussed.