Mutational analysis of the distal control elements. The percentages of GFP-positive, 48-hour embryos obtained after microinjection of deletion constructs are presented. The result obtained with the 4648GM2 construct is shown again as a control. Deletion of the double GATA motif within the distal control region (construct G1m-GM2) completely abolished GFP expression in circulating blood cells of microinjected embryos.