CHARACTERIZATION OF THE EPSTEIN-BARR VIRUS-INDUCIBLE GENE ENCODING THE HUMAN-LEUKOCYTE ADHESION AND ACTIVATION ANTIGEN BLAST-1 (CD48)

BLAST-1 (CD48) (previously referred to as BCM-1 by the Human Gene Nomenclature Committee) is an early-activation-associated membrane glycoprotein expressed on the surface of human leukocytes and induced to a high level following infection of B cells by the Epstein-Barr virus. It is a member of the immunoglobulin superfamily, mediates cell adhesion, and has significant sequence homology to two other adhesion molecules, CD2 and LFA3. Here we report the isolation and characterization of the BLAST-1 gene. The gene is at least 28.6 kb in length, is split into 4 exons, and contains a restriction fragment-length polymorphism. The overall genomic organization is consistent with other members of the immunoglobulin superfamily, in which extracellular immunoglobulinlike domains are encoded by discrete exons. Transcription is initiated at a series of major and minor sites in both normal and tumor-derived lymphoid cells. Appropriately located TATA and CCAAT box sequences were not detected. These characteristics have also been demonstrated for the recently described B-cell-specific genes B29 and CD20. The expression of these genes in B cells may involve the use of multiple promoters and novel transcription initiator-binding proteins. A 1.58-kb genomic DNA fragment, consisting of the 5'-flanking region located immediately upstream of the ATG initiation codon, was able to drive the expression of a reporter gene in an orientation-dependent and tissue-restricted manner.