The evolutionary differentiation of two histone H2A.Z variants in chordates (H2A.Z-1 and H2A.Z-2) is mediated by a stepwise mutation process that affects three amino acid residues
Date
2009-02-04
Authors
Eirin-Lopez, Jose M.
Gonzalez-Romero, Rodrigo
Dryhurst, Deanna
Ishibashi, Toyotaka
Ausio, Juan
Journal Title
Journal ISSN
Volume Title
Publisher
BioMed Central
Abstract
Background: The histone H2A family encompasses the greatest number of core histone variants
of which the replacement variant H2A.Z is currently one of the most heavily studied. No clear
mechanism for the functional variability that H2A.Z imparts to chromatin has yet been proposed.
While most of the past studies have referred to H2A.Z generically as a single protein, in vertebrates
it is a mixture of two protein forms H2A.Z-1 (previously H2A.Z) and H2A.Z-2 (previously H2A.F/
Z or H2A.V) that differ by three amino acids.
Results: We have performed an extensive study on the long-term evolution of H2A.Z across
metazoans with special emphasis on the possible selective mechanisms responsible for the
differentiation between H2A.Z-1 and H2A.Z-2. Our results reveal a common origin of both forms
early in chordate evolution. The evolutionary process responsible for the differentiation involves
refined stepwise mutation change within the codons of the three differential residues. This
eventually led to differences in the intensity of the selective constraints acting upon the different
H2A.Z forms in vertebrates.
Conclusion: The results presented in this work definitively reveal that the existence of H2A.Z-1
and H2A.Z-2 is not a whim of random genetic drift. Our analyses demonstrate that H2A.Z-2 is not
only subject to a strong purifying selection but it is significantly more evolutionarily constrained
than H2A.Z-1. Whether or not the evolutionary drift between H2A.Z-1 and H2A.Z-2 has resulted
in a functional diversification of these proteins awaits further research. Nevertheless, the present
work suggests that in the process of their differently constrained evolutionary pathways, these two
forms may have acquired new or complementary functions.
Description
BioMed Central
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Citation
Eirin-Lopez et al. The evolutionary differentiation of two histone H2A.Z variants in chordates (H2A.Z-1 and H2A.Z-2) is mediated by a stepwise mutation process that affects three aminio acid residues. BMC Evolutionary Biology 2009 9:31