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.