MBE Advance Access published online on April 13, 2006
Molecular Biology and Evolution, doi:10.1093/molbev/msk021
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1 Department of Biochemistry and Microbiology, University of Victoria, Victoria, BC, Canada V8W 3P6; Departamento de Biología Celular y Molecular, Universidade da Coruñ, Campus de A Zapateira s/n, A Coruñ, Spain E-15071
* To whom correspondence should be addressed. Sperm Nuclear Basic Proteins (SNBPs) can be grouped in three main categories: histone type (H), protamine type (P) and protamine-like type (PL). Protamine-like SNBPs represent the most structurally heterogeneous group, consisting of basic proteins which are rich in both lysine and arginine amino acids. The PL proteins replace most of the histones during spermiogenesis, but to a lesser extent than the proteins of the P type. In most instances, PLs coexist in the mature sperm with a full histone complement. The replacement of histones by protamines in the mature sperm is a characteristic feature presented by those taxa located at the uppermost evolutionary branches of protostome and deuterostome evolution, while the histone type of SNBPs is predominantly found in the sperm of taxa which arose early in metazoan evolution; giving rise to the hypothesis that protamines may have evolved through a PL type intermediate from a primitive histone ancestor. The structural similarities observed between PL and H1 proteins, which were first described in bivalve molluscs, provide a unique insight into the evolutionary mechanisms underlying SNBP evolution. Although the evolution of SNBPs has been exhaustively analyzed in the last ten years, the origin of PLs in relation to the evolution of the histone H1 family still remains obscure. In this work we present the first complete gene sequence for two of these genes (PL-III, PL-II/PL-IV) in the mussel Mytilus and analyze the protein evolution of histone H1 and SNBPs, and we provide evidence that indicates that H1 histones and PLs are the direct descendants of an ancient group of ‘orphon’ H1 RD histones which were excluded to solitary genomic regions as early in metazoan evolution as before the differentiation of bilaterians. While the RI H1 lineage evolved following a birth-and-death process, the SNBP lineage has been subject to a purifying process that shifted towards adaptive selection at the time of the differentiation of arginine-rich protamines.
*These authors have contributed equally to this work
Accepted April 1, 2006
Research Article
Common Phylogenetic Origin of Protamine-like (PL) Proteins and Histone H1: Evidence from Bivalve PL Genes
José M. Eirín-López 1 *,
John D. Lewis 2 *,
Le Ann Howe 3,
and
Juan Ausió 2 *
2 Department of Biochemistry and Microbiology, University of Victoria, Victoria, BC, Canada V8W 3P6
3 Department of Biochemistry and Microbiology, University of Victoria, Victoria, BC, Canada V8W 3P6; Present address: Department of Biochemistry and Molecular Biology, University of British Columbia, Life Sciences Centre, Vancouver, BC, Canada V6T 1Z3
Juan Ausió, E-mail: jausio{at}uvic.ca
Abstract
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