Organization of human histone genes

Abstract

We describe the isolation and initial characterization of seven independent lambda Charon 4A recombinant phages which contain human histone genomic sequences (designated lambda HHG). Restriction maps of these clones and localization of the genes coding for histones H2A, H2B, H3, and H4 are presented. The presence of histone encoding regions in the lambda HHG clones was demonstrated by several independent criteria including hybridization with specific DNA probes, hybrid selection/in vitro translation, and hybridization of lambda HHG DNAs to reserve Southern blots containing cytoplasmic RNAs from G1-, S-, and arabinofuranosylcytosine (cytosine arabinoside)-treated S-phase cells. In addition, the lambda HHG DNAs were shown to protect in vivo labeled H4 mRNAs from S1 nuclease digestion. Based on the analysis of the lambda HHG clones, human histone genes appear to be clustered in the genome. However, gene clusters do not seem to be present in identical tandem repeats. The lambda HHG clones described in this report fall into at least three distinct types of arrangement. One of these arrangements contains two coding regions for each of the histones H3 and H4. The arrangement of histone genes in the human genome, therefore, appears to be different from that in the sea urchin and Drosophila genomes in which each of the five histone-encoding regions (H1, H2A, H2B, H3, and H4) is present only once in each tandemly repeated cluster. At least one clone, lambda HHG 41, contains, in addition to the histone genes, a region that hybridizes with a cytoplasmic RNA approximately 330 nucleotides in length. This RNA is not similar in size to known histone-encoding RNAs and is present in the cytoplasm of HeLa cells predominantly in the G1 phase of the cell cycle.