MOLECULAR-CLONING OF BOVINE MB-1 CDNA

Ig-alpha of the B-cell antigen receptor complex forms a heterodimeric structure with Ig-beta on the plasma membrane of B-lymphocytes and is apparently involved in signal transduction during the activation of B- cells. Bovine leukemia virus (BLV) is predominantly a B-cell tropic re trovirus, which induces persistent lymphocytosis and leukemia/lymphoma of B-cell lineage in cattle. To understand the mechanisms of prolifer ation and tumorigenesis of bovine B-cells that are associated with BLV infection, we investigated the B-cell antigen receptor complex, espec ially bovine mb-1 encoding the bovine Ig-alpha protein. We isolated a full-length bovine mb-1 cDNA clone encoding 223 amino acid residues. T he deduced amino acid sequence of the bovine mb-1 showed extensive hom ology with those of human and murine mb-1. The cytoplasmic tail of the bovine mb-1 also contained a consensus motif (D/E-X7-D/E-X2-L/I-X7-Y- X2-L/I) that may interact with the SH2 domain of src-type kinase. Inte restingly, a similar consensus sequence motif was found in the BLV gp3 0(enu), although the overall sequence similarity between bovine mb-1 a nd BLVgp30 was not significant Furthermore, elevated levels of mb-1 tr anscript were detected in various bovine leukemia/lymphoma cell lines. These results indicated that the proliferation of B-cells associated with BLV-infection may be related to abnormal signal transduction thro ugh the B-cell antigen receptor complex.