CLONING AND FUNCTIONAL-CHARACTERIZATION OF EARLY B-CELL FACTOR, A REGULATOR OF LYMPHOCYTE-SPECIFIC GENE-EXPRESSION

Early B-cell factor (EBF) was identified previously as a tissue-specif ic and differentiation stage-specific DNA-binding protein that partici pates in the regulation of the pre-B and B lymphocyte-specific mb-1 ge ne. Partial amino acid sequences obtained from purified EBF were used to isolate cDNA clones, which by multiple criteria encode EBF. The rec ombinant polypeptide formed sequence-specific complexes with the EBF-b inding site in the mb-1 promoter. The cDNA hybridized to multiple tran scripts in pre-B and B-cell lines, but transcripts were not detected a t significant levels in plasmacytoma, T-cell, and nonlymphoid cell lin es. Expression of recombinant EBF in transfected nonlymphoid cells str ongly activated transcription from reporter plasmids containing functi onal EBF-binding sites. Analysis of DNA binding by deletion mutants of EBF identified an amino-terminal cysteine-rich DNA-binding domain lac king obvious sequence similarity to known transcription factors. DNA-b inding assays with cotranslated wild-type and truncated forms of EBF i ndicated that the protein interacts with its site as a homodimer. Dele tions delineated a carboxy-terminal dimerization region containing two repeats of 15 amino acids that show similarity with the dimerization domains of basic-helix-loop-helix proteins. Together, these data sugge st that EBF represents a novel regulator of B lymphocyte-specific gene expression.