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Systematics Section / ASPT

Alvarez-Venegas, Raul [2], Tikhonov, Alexander [1], Orti, Guillermo [2], Moriyama, Etsuko [2], Avramova, Zoya [2].

Evolution of the SET domain: bacterial pathogens, symbionts, and horizontal gene transfer.

Horizontal (or lateral) gene transfer (HGT) can occur between distantly related species. This phenomenon is considered a major force in organismal evolution. However, questions are still surrounding the mechanisms and validity of HGT. Phylogenetic analysis is the best currently available method for establishing incidences of ancient HGT. Here, we report phylogenetic analyses of SET-domain containing proteins in prokaryotes and eukaryotes. The SET domain has been defined as a highly conserved peptide (~130 amino acids) found in epigenetic regulators. Biochemically, the SET peptide carries lysine methylating activity that targets specific lysine residues from the tails of the nucleosomal histones. Because chromatin and histones are signature features of eukaryotes, it has been assumed that SET-genes are only found in eukaryotes. SET-domain coding genes were reported in some bacteria, but their initial identification only in parasitic and symbiotant species was assumed to represent transfer from a eukaryote to a prokaryote. Comprehensive analysis of ~150 fully sequenced bacterial and archebacterial genomes identified ~30 prokaryotic species (pathogenic, symbiotant, and free-living) that carry SET domain coding genes. Even closely related species within the same family can differ by the presence/absence of SET genes. These data seemed to favor HGT. Further analysis, however, revealed SET-gene paralogs in bacteria. Phylogenetic analysis of prokaryotic and eukaryotic SET genes revealed a surprising picture indicating that the SET domain, probably, has a common ancestor. Therefore, the prokaryotic gene(s) did not come from horizontal gene transfer between the eukaryotic and prokaryotic domains of life. However, there are cases of an apparent SET-gene HGT between prokaryotic species, like the SET-genes in Bacillus and Methanosarcina. Finally, we show that in bacteria, a peptide downstream of the SET peptide (named the post-SET domain in eukaryotes) has co-evolved together with the SET domain to perform bacterial gene specific functions.

1 - Protometrix, Inc., Branford, CT 06405, Branford, Connecticut, 06405
2 - University of Nebraska-Lincoln, Biological Sciences, UNL Manter Hall, Lincoln, Nebraska, 68588

horizontal gene transfer.

Presentation Type: Poster
Session: 32-123
Location: Special Event Center (Cliff Lodge)
Date: Tuesday, August 3rd, 2004
Time: 12:30 PM
Abstract ID:901

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