A variant histone H3 is enriched at telomeres in Trypanosoma brucei.
Variant histones play critical roles in transcriptional activation and repression, DNA repair and chromosome segregation. We have identified HTV, a single-copy gene in Trypanosoma brucei encoding a variant form of histone H3 (H3V). H3V is present at discrete nuclear foci that shift over the course of the cell cycle and associate with the mitotic spindle, a pattern of localization reminiscent of that described previously for both mini-chromosomes and telomeres. By combining fluorescence in situ hybridization with indirect immunofluorescence, we confirmed that the H3V foci overlap with a 177-bp repetitive sequence element found predominantly in mini-chromosomes, as well as with the TTAGGG repeats that compose telomeres. Chromatin immunoprecipitation studies, however, reveal that only the telomeric repeat DNA is substantially enriched with H3V. HTV is not essential for viability, mini-chromosome segregation, telomere maintenance or transcriptional silencing at the telomere-proximal expression sites from which bloodstream-form T. brucei controls antigenic variation. We propose that H3V represents a novel class of histone H3 variant, a finding that has evolutionary implications.
Lowell
Joanna E
JE
Laboratory of Molecular Parasitology, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA.
Cross
George A M
GA
D000595:Amino Acid Sequence; D000818:Animals; D002453:Cell Cycle; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D002470:Cell Survival; D047369:Chromatin Immunoprecipitation; D002875:Chromosomes / Q000648:ultrastructure; D003001:Cloning, Molecular; D004247:DNA / Q000378:metabolism; D004260:DNA Repair; D019084:Fluorescent Antibody Technique, Indirect; D020868:Gene Silencing; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006657:Histones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017403:In Situ Hybridization; D017404:In Situ Hybridization, Fluorescence; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009154:Mutation; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D008941:Spindle Apparatus; D016615:Telomere / Q000648:ultrastructure*; D014346:Trypanosoma brucei brucei
D006657:Histones; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D004247:DNA