摘要：

The variable portion of an immunoglobulin heavy chain gene is assembled from at least three discontinuous segments of DNA, the V, D and J regions. We have characterized a 30 kb segment of the human genome that plays a critical role in the formation of this variable region as well as in the expression of the two heavy chains that appear earliest in immunocyte ontogeny, the μ and δ chains. This region encodes nine J-like segments, an interspersed D segment, recombination signals and the genes responsible for the production of both μ and δ heavy chains. Six of the nine germline J-like genes appear to be active and easily account for most of the known human heavy chain amino acid sequences. Three of the J-like genes are pseudogenes. The large number of human J region genes and, hence, their greater potential for generating diversity as compared to the that of the mouse J region genes appears to result from recent genetic duplications. To assess this potential, we have analyzed two recombinant genes involving this region. One of these, a V—D—J recombinant, is likely to be an active gene; the other, an aberrant D—J recombinant. A comparison of the structures of these D regions raises the possibility that they are mosaics formed by recombination between D segments.

展开