Differential expression of XAP5, a candidate disease gene.

We have isolated a full-length cDNA corresponding to the XAP5 gene in Xq28. An unusual feature of the cDNA is that it contains runs of CCG repeats in the 5' untranslated region, typical of genes that exhibit anticipation. It has a striking pattern of differential expression and is greatly enhanced in various fetal tissues. This predicted protein encodes a unique 339-amino-acid polypeptide that contains a large percentage of highly charged residues and a possible nuclear localization signal. A comparison to genomic sequence shows that XAP-5 comprises 13 exons spanning 6.5 kb. An examination of the human population indicates that the longest CCG run is polymorphic and varies in length from 8 to 12 repeats.