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Mol. Cell. Biol., 07 1995, 3848-3856, Vol 15, No. 7
JH Millonig, JA Emerson, JM Levorse and SM Tilghman
The mouse alpha-fetoprotein (AFP) gene is transcribed at high levels in the
visceral endoderm of the yolk sac and fetal liver and at much lower rates
in the endoderm of the fetal gut. Expression of the gene in vivo requires
the presence of at least one of three enhancers which lie in its 5'
flanking region. In this report, we establish that the most distal AFP
enhancer directed consistent expression of a linked AFP minigene in all
three endodermal tissues in transgenic mice. The enhancer is composed of
three domains, each of which is essential for full enhancer function by
transient transfection assays. DNase I footprinting identified three
regions of the enhancer which are protected by human hepatoma nuclear
extracts, one of which corresponded to a consensus site for HNF-3 binding.
Site-directed mutations in this site caused a 10-fold reduction in enhancer
function by transient transfection. In transgenic mice, however, the
mutation resulted in sporadic expression of the transgene, dependent on the
site of integration. A similar acquisition of position-dependent sporadic
expression of the transgene was observed with a mutation in a second
protein binding site, despite the fact that this mutation had very little
effect on enhancer function as assessed by transient transfection. These
studies underscore the value of examining the functions of specific protein
binding sites in vivo.
Copyright © 1995, American Society for Microbiology
Molecular analysis of the distal enhancer of the mouse alpha- fetoprotein gene
Howard Hughes Medical Institute, Princeton University, New Jersey 08544, USA.
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