Fig. 4.

Fusion genes redirect gene expression in transgenic mice. The natural genes: human growth hormone, mouse metallothionein-I, rat elastase-1, and SV40 T antigen were expressed in the tissues indicated to the right. When their controlling elements (promoter/enhancer) were fused to different structural genes, then the expression of the structural gene was redirected as dictated by the promoter/enhancer specificity. The solid boxes represent exons, the open boxes introns, the line represents the 5′ flanking sequences including the promoter. The solid symbols in the promoter represent the enhancer elements; there are four functional metal regulatory elements in the mouse metallothionein promoter (circles), probably only one cell-specific enhancer element in the elastase promoter (hexagon), and two 72 bp repeats of the SV40 enhancer (squares). All fusions were made between the cap site (+ 1) and the initiation codon of the respective genes. The genes are not drawn to scale.