The structure of the human histone genes: clustered but not tandemly repeated

We have isolated five clones containing human histone genes from a human genomic DNA library, using a cloned X. laevis histone H4 cDNA probe (pX1ch4). Each genomic clone has been mapped and the locations of the histone genes have been determined by blot hybridization and hybridization-selection of human histone mRNA. In contrast to the organization of previously characterized histone genes, the human histone genes are clustered in the genome but are not arranged into recognizable repeating units. The extreme lack of organization of the human histone genes may reflect the diminished requirement for rapid synthesis of large quantities of histone proteins during mammalian early development.