Duplicated zinc finger protein genes on the proximal short arm of the human X chromosome: isolation, characterization and X-inactivation studies

Two highly similar zinc finger genes, ZXDA (Zinc finger, X-linked, Duplicated) and ZXDB, have been isolated and characterized. Both map to the proximal short arm region of the human X chromosome, near locus DXS422 in Xp11.21. Both genes are expressed in several human tissues, revealing a approximately 6.5 kb mRNA by Northern blot hybridization, and both are subject to X-inactivation. A comparison of 1.2 kb of cDNA sequence from a single exon in the open reading frames of the two genes reveals 98.7% identity in nucleotide sequence. The predicted proteins include at least ten tandem C2-H2 zinc finger motifs. When cDNA probes from different parts of the genes are hybridized to a blot of different animal DNAs, two bands are seen in all placental mammals, suggesting that the duplication predates the radiation of placental mammals and is highly conserved. Furthermore, under conditions of lowered stringency, additional bands are seen in several species, suggesting that the two genes reported here may be members of a larger zinc finger gene family.