LONG-RANGE SEQUENCE-ANALYSIS IN XQ28 - 13 KNOWN AND 6 CANDIDATE GENESIN 219.4 KB OF HIGH GC DNA BETWEEN THE RCP GCP AND GGPD LOCI/

DNA comprising 219 447 bp was sequenced in nine cosmids and verified a t >99.9% precision, Of the standard repetitive elements, 187 Alus make up 20.6% of the sequence, but there were only 27 MERs (2.9%) and 17 L 1 fragments (1.6%), This may be characteristic of such high GC (57%) r egions, The sequence also includes an 11.3 kb tract duplicated with 99 .2% identity at a distance of 38 kb, The region is 80-90% transcribed and 12.5% translated, Thirteen known genes and their exon-intron borde rs are all accurately predicted at least in part by GRAIL programs, as are six additional genes, From centromere to telomere, the orientatio n of transcription varies among the first eight genes, then runs centr omeric to telomeric far the next five, and is in the opposite sense fo r the last six, Eighteen of the 19 genes are associated with CpG islan ds, Two islands are exact copies in the 11.3 kb repeat units, and coul d thus give rise to double dosage levels of an X-linked gene, Another island is associated with two genes transcribed in opposite directions , From the sequence data, three genes and their exon structure are inf erred, One of them, previously associated with HEX2, is shown to be a different gene unrelated to hexokinases; a second gene, previously kno wn by an EST, is plexin, from its 65.5% identity with the Xenopus anal og; and a third is a subunit of a vacuolar H-ATPase, and is named VATP S1.