GENES IN ONE MEGABASE OF THE HLA CLASS-I REGION

To define the gene content of the HLA class I region, cDNA selection w as applied to three overlapping yeast artificial chromosomes (YACs) th at spanned 1 megabase (Mb) of this region of the human major histocomp atibility complex. These YACs extended from the region centromeric to HLA-E to the region telomeric to HLA-F. In addition to the recognized class I genes and pseudogenes and the anonymous non-class-I genes desc ribed recently by us and others, 20 additional anonymous cDNA clones w ere identified from this 1-Mb region. We also identified a long repeti tive DNA element in the region between HLA-B and HLA-E. Homologues of this element were located at several sites in the human genome outside of the HLA complex. The portion of the HLA class I region represented by these YACs shows an average gene density as high as the class II a nd class III regions. Thus, the high gene density portion of the HLA c omplex is extended to more than 3 Mb.