ISOLATION OF A CLONE PARTIALLY ENCODING HILL KANGAROO X-LINKED HYPOXANTHINE PHOSPHORIBOSYLTRANSFERASE - SEX-DIFFERENCES IN METHYLATION IN THE BODY OF THE GENE

An X-linked clone encoding exons 4-9 of the hypoxanthine phosphoribosy ltransferase (HPRT) gene was isolated from a kangaroo (Macropus robust us: Marsupialia) lambdaEMBL4 genomic library. Sequence similarity betw een the kangaroo and eutherian HPRT coding sequences was high; however , intron sizes varied significantly between the kangaroo and other eut herian species. HpaII and HhaI sites in the body of the gene were gene rally hypermethylated in vivo on the active, relative to the inactive X, with sites within intron 3 showing essentially complete corresponde nce of activity with methylation and inactivity with unmethylation. At approximately 5 kb downstream from the gene, a switch to unmethylatio n of active X-linked sites occurred. This switch occurred within a clu ster of HpaII and HhaI sites that may represent a CG island associated with a subsequent gene.