for EBF, together with some flanking sequences, was 
found to confer on a heterologous promoter a pre-B 
and B cell-specific pattern of activity. Thus the dis- 
tribution and activity of EBF in various lymphoid 
and nonlymphoid cell lines parallels precisely the 
developmental expression pattern of the endoge- 
nous mb-1 gene. A similar DNA-binding activity was 
also identified by Dr. Harinder Singh's laboratory 
(HHMI, University of Chicago). 
Recently Dr. Grosschedl's laboratory purified EBF 
to near homogeneity and showed that this DNA- 
binding activity consists of polypeptides of 65 kDa. 
Partial amino acid sequences were derived from 
purified EBF and used to design oligonucleotide 
primers for the amplification of specific cDNAs 
from a pre-B cell cDNA library. Overlapping cDNA 
clones that encoded a protein of 64 kDa were iso- 
lated. Three sets of experimental data suggested that 
the isolated cDNAs encode EBF. First, the gene repre- 
sented by the cDNA clones is expressed in pre-B and 
B cells but not in late-stage B cells, T cells, or the 
nonlymphoid cells examined. Second, the protein 
encoded by the cDNA has the same DNA-binding 
specificity as purified EBF. Third, forced expression 
of the cDNA clone in a nonlymphoid cell line trans- 
activated a reporter gene construct in an EBF- 
binding site-dependent manner. Analysis of the 
amino acid sequence of EBF indicated that this 
lineage-specific protein is encoded by a novel gene 
with no obvious relative in the current protein data- 
base. 
Isolation and Characterization of cDNAs 
Encoding LEF-1 
To identify novel lymphocyte-specific regulators 
of gene expression, Dr. Grosschedl's laboratory iso- 
lated, by differential screening of a pre-B cell minus 
erythroid cell cDNA library, cDNA clones that are 
expressed specifically in lymphocytes. One of these 
cDNA clones encodes a pre-B and T cell-specific 
DNA-binding protein with homology to the chromo- 
somal nonhistone high-mobility group protein 
HMG-1 and to regulators of cell specialization. The 
lymphoid-specific DNA-binding protein LEF- 1 (lym- 
phoid enhancer-binding factor 1 ) was found to bind 
a functionally important nucleotide sequence in the 
enhancer associated with the T cell antigen receptor 
(TCR) a gene. The role of LEF- 1 in regulating TCR a 
enhancer function was funher shown by transactiva- 
tion in B cells that normally do not express LEF-1 . In 
collaboration with Dr. Uta Francke (HHMI, Stanford 
University), the LEF-1 gene was mapped to human 
chromosome 4 (q23-q25) and mouse chromosome 
3 near the Egf locus. 
The DNA-binding domain of LEF- 1 was delineated 
to a 93-amino acid region, the HMG domain, which 
has homology to other members of the HMG family 
of proteins. Several amino acids that are conserved 
among various members of this family were shown 
to be important for DNA binding. Analysis of the 
DNA-binding properties of the HMG domain of 
LEF- 1 indicated that this protein-DNA interaction is 
characterized by a high binding affinity but modest 
sequence specificity. Moreover, methylation inter- 
ference data and replacement of A T base pairs in the 
LEF-1 -binding site with I-C base pairs suggested 
that DNA recognition by the HMG domain of LEF-1 
occurs primarily in the minor groove of the DNA 
double helix. Finally, DNA binding by LEF-1 was 
found to induce a sharp bend of ~ 1 30° in the DNA 
helix. These hallmarks for DNA binding by the 
HMG domain of LEF-1 were also extended to 
the HMG domain of the mammalian testis-determin- 
ing factor SRY. 
Dr. Grosschedl's laboratory examined possible 
regulatory roles of HMG domain-induced DNA 
bending and found that LEF- 1 can function in a man- 
ner similar to the bacterial integration host factor 
(IHF). In a site-specific recombination assay in vi- 
tro, LEF-1 could functionally replace IHF in its role 
to align spatially widely separated binding sites for 
integrase protein. Thus LEF-1 has the potential of 
facilitating the communication between proteins 
bound at distant sites and may provide an "architec- 
tural" role in the assembly of higher-order nucleo- 
protein structures. 
Dr. Grosschedl is also Associate Professor of Mi- 
crobiology and Immunology and of Biochemistry 
and Biophysics at the University of California, 
San Francisco. 
Articles 
Giese, K., Amsterdam, A., and Grosschedl, R. 
1991- DNA-binding properties of the HMG do- 
main of the lymphoid-specific transcriptional reg- 
ulator LEF-1. Genes Dev 5:2567-2578. 
Giese, K., Cox, J., and Grosschedl, R. 1992. The 
HMG domain of lymphoid enhancer factor 1 
bends DNA and facilitates assembly of functional 
nucleoprotein structures. Cell 69:185-195. 
Hagman, J., Travis, A., and Grosschedl, R. 1991 . A 
novel lineage-specific nuclear factor regulates 
mb-1 gene transcription at the early stages of B 
cell differentiation. EMBO f 10:3409-3417. 
Matsuuchi, L., Gold, M.R., Travis, A., Grosschedl, 
R., DeFranco, A.L., and Kelly, R.B. 1992. The 
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