Combinatorial control of positive and negative, upstream and intragenic regulatory DNA domains of the mouse alpha 1-foetoprotein gene.

Chimeric constructions were isolated, which contained DNA segments from the 5' flanking region of the mouse AFP gene, placed upstream the bacterial chloramphenicol acetyltransferase gene. Their activity was tested after transfection into different cells. This analysis led to the discovery of two new regulatory elements of the AFP gene. One element is located in the 5' proximal region flanking the transcriptional start site and acts in a highly cell type-specific manner: it shows an enhancer activity in AFP-producing hepatoma cells, but this proximal enhancer activity is replaced by a strong negative activity in fibroblasts. The second element is located in the intragenic region; it exhibits a negative activity in AFP-producing hepatoma cells where it efficiently antagonizes the proximal enhancer activity; however, this negative effect is overriden by the combined action of the proximal enhancer (identified in this work) and of the distal enhancer identified previously by Godbout and coworkers.