The HLA class I genes are located within a llion-base pair (2-Mbp) region constituting the telomeric of the human major histocompatibility complex. The large erity of the class I sequences, including the HLA-A, -E, -F, -G genes, is found within the telomeric 1 Mbp. We report the isolation and characterization of yeast artificial chro ome (YAC) clones that span a contiguous region of >1.2 p and include 14 of the 18 characterized class I sequences. triction enzyme mapping and the use of locus-specific hes have allowed all of the class I genes and sequences to be ared and positioned within the region. In addition, the criptional orientation of the four class I genes has been mined. Using probes derived from the ends of YAC inserts from class I pseudogenes, we describe a highly polymor c between the HLA-A and HLA-G genes. This region pears to be deleted in certain HLA haplotypes, shortening the tance between HLA-A and HLA-G by >50 kilobase pairs p). As part of the characterization of the YAC clones, unique sequence probes derived from the ends of each YAC rt were identified. When combined with probes derived from HLA genes and pseudogenes, 25 locus-specific probes ning the 1.2-Mbp region have been identified for an rage of 1 probe every 48 kbp.