title: Differences in evolutionary pressure acting within highly conserved ortholog groups.
abstract: BACKGROUND
  In highly conserved widely distributed ortholog groups, the main evolutionary force is assumed to be purifying selection that enforces sequence conservation, with most divergence occurring by accumulation of neutral substitutions. Using a set of ortholog groups from prokaryotes, with a single representative in each studied organism, we asked the question if this evolutionary pressure is acting similarly on different subgroups of orthologs defined as major lineages (e.g. Proteobacteria or Firmicutes).
  
  
  RESULTS
  Using correlations in entropy measures as a proxy for evolutionary pressure, we observed two distinct behaviors within our ortholog collection. The first subset of ortholog groups, called here informational, consisted mostly of proteins associated with information processing (i.e. translation, transcription, DNA replication) and the second, the non-informational ortholog groups, mostly comprised of proteins involved in metabolic pathways. The evolutionary pressure acting on non-informational proteins is more uniform relative to their informational counterparts. The non-informational proteins show higher level of correlation between entropy profiles and more uniformity across subgroups.
  
  
  CONCLUSIONS
  The low correlation of entropy profiles in the informational ortholog groups suggest that the evolutionary pressure acting on the informational ortholog groups is not uniform across different clades considered this study. This might suggest "fine-tuning" of informational proteins in each lineage leading to lineage-specific differences in selection. This, in turn, could make these proteins less exchangeable between lineages. In contrast, the uniformity of the selective pressure acting on the non-informational groups might allow the exchange of the genetic material via lateral gene transfer.
authors.affiliation: National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA. przytyck@ncbi.nlm.nih.gov
authors.forename: Teresa M
authors.initials: TM
authors.lastname: Przytycka
authors.forename: Raja
authors.initials: R
authors.lastname: Jothi
authors.forename: L
authors.initials: L
authors.lastname: Aravind
authors.forename: David J
authors.initials: DJ
authors.lastname: Lipman
mesh_terms: D001105:Archaea / Q000235:genetics*; D017124:Conserved Sequence / Q000235:genetics*; D019143:Evolution, Molecular; D022761:Gene Transfer, Horizontal; D019766:Genes, Archaeal / Q000235:genetics; D005798:Genes, Bacterial / Q000235:genetics; D006094:Gram-Positive Bacteria / Q000235:genetics*; D020560:Proteobacteria / Q000235:genetics*