MBE Advance Access published online on December 23, 2003
Molecular Biology and Evolution, doi:10.1093/molbev/msh048
Molecular Biology and Evolution © Society for Molecular Biology and Evolution 2003; all rights reserved
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1 Department of Biological Sciences, Smith College, Northampton MA, 01063, USA; Program in Organismic and Evolutionary Biology, University of Massachusetts-Amherst, Amherst MA, 01003, USA
* To whom correspondence should be addressed. E-mail: Lkatz{at}Smith.edu.
The accumulation of divergent histone H4 amino acid sequences within and between ciliate lineages challenges traditional views of the evolution of this essential eukaryotic protein. We analyzed histone H4 sequences from 13 species of ciliates and compared these data to sequences from well-sampled eukaryotic clades. Ciliate histone H4s differ from one another at as many as 46% of their amino acids, in contrast with the highly conserved character of this protein in most other eukaryotes. Equally striking, we find paralogs of histone H4 within ciliate genomes that differ by up to 25% of their amino acids, while paralogs in other eukaryotes share identical or nearly identical amino acid sequences. Moreover, the most divergent H4 proteins within ciliates are found in the lineages with highly processed macronuclear genomes. Our analyses demonstrate that the dual nature of ciliate genomes - the presence of a ‘germline’ micronucleus and a ‘somatic’ macronucleus within each cell - allowed the dramatic variation in ciliate histone genes by altering functional constraints or enabling adaptive evolution of the histone H4 protein, or both. Key Words:
Protein evolution, histone H4, ciliates, macronucleus, chromosomal rearrangements
© 2003 Society for Molecular Biology and Evolution
Original Articles
Dramatic Diversity of Ciliate Histone H4 Genes Revealed by Comparisons of Patterns of Substitutions and Paralog Divergences among Eukaryotes
2 Program in Organismic and Evolutionary Biology, University of Massachusetts-Amherst, Amherst MA, 01003, USA
3 Department of Biological Sciences, Smith College, Northampton MA, 01063, USA
4 Bioinformatics Research Center, Department of Statistics, North Carolina State University, Raleigh NC, 27695, USA
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