evolutionarily conserved. In addition, the two pro- 
teins are nearly identical in their mjr-related helbc- 
turn-helix motifs, which in turn are similar to that 
found in TFE3. This region is capable of directing 
the formation of heterodimers between the two dif- 
ferent p£5-binding proteins. Each protein activates 
transcription as a GAL4 fusion protein, and the 
transcription activation domains determined in this 
manner also map to regions of the proteins that are 
distinct from their dimerization motifs. One of them 
is capable, when expressed on its own, of acting as 
a potent transcriptional activator in yeast. 
The IgH enhancer has provided a fascinating 
model for tissue-specific transcription regulation. 
PUBLICATIONS 
A ubiquitous positive transcription factor, TFE3, 
binds the enhancer next to a site that itself binds a 
family of proteins, one (or many) of which appar- 
ently represses the activity of TFE3 in non-B cells. 
It is likely that TFE3 makes contact with its neigh- 
bor proteins and that this interaction somehow 
helps mediate cell-type-specific activity of the en- 
hancer. With cDNAs that encode these proteins 
now available, many of the aspects of this model 
can be tested directly. 
Dr. Kadesch is also Assistant Professor of Human 
Genetics at the University of Pennsylvania School of 
Medicine. 
Articles 
Henthorn, PS., Raducha, M., Kadesch, T, Weiss, M.J., and Harris, H. 1988. Sequence and characterization of 
the human intestinal alkaline phosphatase gene. J Biol Chem 263:12011-12019. 
Henthorn, PS., Zervos, P., Raducha, M., Harris, H., and Kadesch, T. 1988. Expression of a human placental al- 
kaline phosphatase gene in transfected cells: use as a reporter for studies of gene expression. Proc Natl 
Acad Sci USA 85:6342-6346. 
Weiss, M.J., Ray, K., Henthorn, PS., Lamb, B., Kadesch, T, and Harris, H. 1988. Structure of the human 
liver/bone/kidney alkaline phosphatase gene. J Biol Chem 263:12002-12010. 
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