A BOUNDARY OF LONG-RANGE G+C-PERCENT MOSAIC DOMAINS IN THE HUMAN MHC LOCUS - PSEUDOAUTOSOMAL BOUNDARY-LIKE SEQUENCE EXISTS NEAR THE BOUNDARY

The human genome is composed of long-range G+C% (GC%) mosaic structures related to chromosome bands. We found the human MHC locus to be an example of megabase-level GC% mosaic structures and predicted a possible boundary of the megabase-level domains within an undercharacterized 450-kb region harboring the junction of MHC classes II and III. Chromosome walking of the 450-kb region and base compositional analysis precisely located the boundary of the mosaic domains, disclosing a sharp GC% transition. Near the transition point there was a 20-kb dense ALu cluster, a 30-kb dense LINE-1 cluster, and a sequence highly homologous with the pseudoautosomal boundary of the short arms of human sex chromosomes (PAB1X and PAB1Y); PAB1X and PAB1Y are the interface between sex-specific and pseudoautosomal regions. Many PAB1XY-like sequences (PABLs) were detected by hybridization against genomic DNA, and the new sequences defined the complete form of PABLs to be about 650 nt. (C) 1995 Academic Press, Inc.