The D4Z4 repeat contains a strong transcriptional enhancer. (A) Schematic representation of the D4Z4 repeat in its chromosome 4q35 environment. The SLC25A4 (previously known as ANT1), FRG1, and FRG2 genes are shown as gray rectangles. Telomeric and D4Z4 repeats are shown as circles and triangles, respectively. A scaffold/matrix attachment region depicted as FR-MAR (dark gray) is located between the genes and the D4Z4 array. (B) The D4Z4 repeat unit contains a strong transcriptional enhancer. The transcriptional effect of the D4Z4 repeat unit and its deletion fragments was tested 48 h after transfection. The enhancer strength is quantified relative to the luciferase activity generated with the SV40 enhancer. The numbers refer to the nucleotide positions starting from the upstream KpnI restriction site. (C) The minimal D4Z4 enhancer is neither species nor tissue specific. The effect of the minimal D4Z4 enhancer was tested in human primary myoblasts, HeLa cells, the human rhabdomyosarcoma cell line RMS, and the murine myoblast cell line C2C12. Luciferase activity is shown relative to that obtained with the SV40 enhancer.
