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MBE Advance Access published online on October 18, 2007
Molecular Biology and Evolution, doi:10.1093/molbev/msm232
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© The Author 2007. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Research Article

Euglena Light-Harvesting Complexes are Encoded by Multifarious Polyprotein mRNAs that Evolve in Concert

Adam G. Koziol and Dion G. Durnford*

Department of Biology, University of New Brunswick, Fredericton, NB, Canada, E3B 5A3

* Author for correspondence; D.G. Durnford, durnford{at}unb.ca, Phone: 506-452-6207, Fax: 506-453-3583

Received for publication August 10, 2007. Revision received September 28, 2007. Accepted for publication October 11, 2007.

Light-harvesting complexes (LHCs) are a superfamily of chlorophyll and carotenoid-binding proteins that are responsible for the capture of light energy and its transfer to the photosynthetic reaction centers. Unlike those of most eukaryotes, the LHCs of Euglena gracilis are translated from large mRNAs, producing polyprotein precursors consisting of multiple concatenated LHC subunits that are separated by conserved decapeptide linkers. These precursors are post-translationally targeted to the chloroplast and cleaved into individual proteins. We analyzed expressed sequence tags from Euglena to further characterize the structural features of the LHC polyprotein-coding genes and to examine the evolution of this multigene family. Of the 19 different LHC transcriptional units we detected, 17 encoded polyproteins composed of both tandem and non-tandem repeats of LHC subunits; organizations that likely occurred through unequal crossing-over. Of the two non-polyprotein encoding Lhc transcripts detected, one evolved from the truncation of a polyprotein-coding gene. Duplication of LHC polyprotein coding genes was particularly important in the LHCI gene family where multiple paralogous sequences were detected. Intriguingly, several of the individual LHC coding subunits both within and between transcriptional units appeared to be evolving in concert, suggesting that gene conversion has been a significant mechanism for Lhc evolution in Euglena.

Key Words: Light-harvesting complex • Concerted evolution • polyprotein • Euglena


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