BIASED USAGE OF 2 RESTRICTED VH GENE SEGMENTS IN VH REPLACEMENT

AT8-1-12-5, an intracytoplasmic gamma2b-producing (mu-gamma2b+) pre-B cell line transformed with Abelson murine leukemia virus continuously generated intracytoplasmic mu, gamma2b-producing (mu+gamma2b+) cells during propagation in culture. Southern blotting, DNA cloning and sequence analysis showed that these mu+gamma2b+ cells were generated from the mu-gamma2b+ pre-B cells by V(H) replacement events. The gene segments involved in these replacement events were restricted to only two V(H) gene segments, V(H)7.1 (V(H)7183 family) and V(H)6.2 (V(H)Q52 family). Cell staining using the monoclonal anti-V(H) 141 antibody 3-5-6f that specifically recognized the V(H)6.2 but not V(H)7.1 gene products indicated that half of the V(H) replacement events occurring in AT8-1-12-5 used the V(H)6.2 gene segment. Deletion mapping indicated that the incoming V(H) gene segments, V(H)7.1 and V(H)6.2 were proximal to the resident V(H) gene segment, V(H)12.5 (V(H)7183 family). These results provided direct evidence of the biased usage of V(H) gene segments in V(H) replacement and have several implications for the mechanisms of V(H) replacement.