title: Evolutionary history of selenocysteine incorporation from the perspective of SECIS binding proteins.
abstract: BACKGROUND
  The co-translational incorporation of selenocysteine into nascent polypeptides by recoding the UGA stop codon occurs in all domains of life. In eukaryotes, this event requires at least three specific factors: SECIS binding protein 2 (SBP2), a specific translation elongation factor (eEFSec), selenocysteinyl tRNA, and a cis-acting selenocysteine insertion sequence (SECIS) element in selenoprotein mRNAs. While the phylogenetic relationships of selenoprotein families and the evolution of selenocysteine usage are well documented, the evolutionary history of SECIS binding proteins has not been explored.
  
  
  RESULTS
  In this report we present a phylogeny of the eukaryotic SECIS binding protein family which includes SBP2 and a related protein we herein term SBP2L. Here we show that SBP2L is an SBP2 paralogue in vertebrates and is the only form of SECIS binding protein in invertebrate deuterostomes, suggesting a key role in Sec incorporation in these organisms, but an SBP2/SBP2L fusion protein is unable to support Sec incorporation in vitro. An in-depth phylogenetic analysis of the conserved L7Ae RNA binding domain suggests an ancestral relationship with ribosomal protein L30. In addition, we describe the emergence of a motif upstream of the SBP2 RNA binding domain that shares significant similarity with a motif within the pseudouridine synthase Cbf5.
  
  
  CONCLUSIONS
  Our analysis suggests that SECIS binding proteins arose once in evolution but diverged significantly in multiple lineages. In addition, likely due to a gene duplication event in the early vertebrate lineage, SBP2 and SBP2L are paralogous in vertebrates.
authors.affiliation: Department of Molecular Genetics, Microbiology, and Immunology, Graduate School of Biomedical Sciences, University of Medicine and Dentistry of New Jersey - Robert Wood Johnson Medical School, Piscataway, NJ, USA. donovaje@umdnj.edu
authors.forename: Jesse
authors.initials: J
authors.lastname: Donovan
authors.forename: Paul R
authors.initials: PR
authors.lastname: Copeland
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019843:Archaeal Proteins / Q000235:genetics; D005057:Eukaryotic Cells / Q000378:metabolism; D019143:Evolution, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D016601:RNA-Binding Proteins / Q000378:metabolism*; D012269:Ribosomal Proteins / Q000235:genetics; D017279:Selenocysteine; D051140:Selenoproteins / Q000235:genetics*; D016415:Sequence Alignment
chemical_list: D019843:Archaeal Proteins; D016601:RNA-Binding Proteins; D012269:Ribosomal Proteins; D051140:Selenoproteins; C035201:ribosomal protein L30; D017279:Selenocysteine