CHROMOSOMAL LOCALIZATION OF THE HUMAN HISTONE H2A.X GENE TO 11Q23.2-Q23.3 BY FLUORESCENCE IN-SITU HYBRIDIZATION

The human histone H2A.X gene is unusual in that its transcripts are al ternatively processed to yield two species, one a 0.6-kb replication-l inked histone mRNA and the other a 1.6-kb polyadenylated mRNA. The H2A .X gene has been localized by fluorescence in situ hybridization to ch romosome 11q23.2-q23.3, away from the known clusters of human histone genes on chromosomes 1, 6, and 12. Assignment to chromosome 11 was sub stantiated by analysis of human-hamster somatic cell hybrid lines. As this work was being completed, an 89-bps sequence overlap was found be tween the downstream regions of the H2A.X gene and the recently sequen ced hydroxymethylbilane (HMB)-synthase gene. The H2A.X and HMB-synthas e genes have an unusual arrangement, being transcribed towards each ot her with their polyadenylation sites 330 bp apart. In addition the HMB -synthase gene contains constitutive and erythroid specific promoters. K562, an erythroid cell line, was found to contain a high concentrati on of the 1.6-kb polyadenylated H2A.X mRNA.