HUMAN PSEUDOAUTOSOMAL BOUNDARY-LIKE SEQUENCES - EXPRESSION AND INVOLVEMENT IN EVOLUTIONARY FORMATION OF THE PRESENT-DAY PSEUDOAUTOSOMAL BOUNDARY OF HUMAN SEX-CHROMOSOMES

The human genome is composed of long-range mosaic structures of G+C% ( GC%), which are thought to be related to chromosome bands. We previous ly identified a boundary of Mb-level domains of GC% mosaic structures in the human major histocompatibility complex (MHC) and found in the d omain boundary a sequence very similar to pseudoautosomal boundary (PA B) sequences of human sex chromosomes. We designated it 'PABL' and fou nd many PABLs in the human genome. By analysis of six genomic and six transcribed PABLs, a core and consensus sequence of about 650 nt was d efined; the 3'- and 5'-edges of the PABLs were strictly conserved. Nor thern blot analysis showed sizes of PABL transcripts to be 5-10 kb in length. Divergence time of PABLs was estimated to be 60-120 million ye ars ago by analysis of human PABLs and PABXY1 of seven primates, and t he evolutionary rates deduced showed PABLs to have been under selectiv e constraints. A model for evolutionary formation of the present pseud oautosomal boundary was proposed by postulation of illegitimate recomb ination between two PABLs.