| Summary: | <p>Abstract</p> <p>Background</p> <p>EFL (or elongation factor-like) is a member of the translation superfamily of GTPase proteins. It is restricted to eukaryotes, where it is found in a punctate distribution that is almost mutually exclusive with elongation factor-1 alpha (EF-1α). EF-1α is a core translation factor previously thought to be essential in eukaryotes, so its relationship to EFL has prompted the suggestion that EFL has spread by horizontal or lateral gene transfer (HGT or LGT) and replaced EF-1α multiple times. Among green algae, trebouxiophyceans and chlorophyceans have EFL, but the ulvophycean <it>Acetabularia </it>and the sister group to green algae, land plants, have EF-1α. This distribution singles out green algae as a particularly promising group to understand the origin of EFL and the effects of its presence on EF-1α.</p> <p>Results</p> <p>We have sampled all major lineages of green algae for both EFL and EF-1α. EFL is unexpectedly broad in its distribution, being found in all green algal lineages (chlorophyceans, trebouxiophyceans, ulvophyceans, prasinophyceans, and mesostigmatophyceans), except charophyceans and the genus <it>Acetabularia</it>. The presence of EFL in the genus <it>Mesostigma </it>and EF-1α in <it>Acetabularia </it>are of particular interest, since the opposite is true of all their closest relatives. The phylogeny of EFL is poorly resolved, but the <it>Acetabularia </it>EF-1α is clearly related to homologues from land plants and charophyceans, demonstrating that EF-1α was present in the common ancestor of the green lineage.</p> <p>Conclusion</p> <p>The distribution of EFL and EF-1α in the green lineage is not consistent with the phylogeny of the organisms, indicating a complex history of both genes. Overall, we suggest that after the introduction of EFL (in the ancestor of green algae or earlier), both genes co-existed in green algal genomes for some time before one or the other was lost on multiple occasions.</p>
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