Mol Cell Biol, June 1998, p. 3130-3139, Vol. 18, No. 6
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Department of Biology, University of California, San Diego, La Jolla, California 92093,1 and Department of Immunology, Erasmus University/University Hospital Dijkzigt, Rotterdam, The Netherlands2
Received 31 October 1997/Returned for modification 12 December 1997/Accepted 26 February 1998
Proteins of the basic helix-loop-helix (bHLH) family are required for a number of different developmental pathways, including neurogenesis, lymphopoiesis, myogenesis, and sex determination. Using a yeast two-hybrid screen, we have identified a new bHLH transcription factor, ABF-1, from a human B-cell cDNA library. Within the bHLH region, ABF-1 shows a remarkable conservation with other HLH proteins, including tal-1, NeuroD, and paraxis. Its expression pattern is restricted to a subset of lymphoid tissues, Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines, and activated human B cells. ABF-1 is capable of binding an E-box element either as a homodimer or as a heterodimer with E2A. Furthermore, a heterodimeric complex containing ABF-1 and E2A can be detected in EBV-immortalized lymphoblastoid cell lines. ABF-1 contains a transcriptional repression domain and is capable of inhibiting the transactivation capability of E47 in mammalian cells. ABF-1 represents the first example of a B-cell-restricted bHLH protein, and its expression pattern suggests that ABF-1 may play a role in regulating antigen-dependent B-cell differentiation.
Present address: Center for Blood Research, Harvard Medical School,
Boston, MA 02115.
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