title: A novel mechanism for translation initiation operates in haloarchaea.
abstract: Four different mechanisms for translation initiation are known, i.e. one prokaryotic mechanism involving a Shine-Dalgarno sequence, two eukaryotic mechanisms relying on ribosomal scanning or internal ribosomal entry sites, and one mechanism acting on leaderless transcripts. Recently it was reported that the majority of haloarchaeal transcripts is leaderless and that most leadered transcripts are devoid of a Shine-Dalgarno sequence, excluding the operation of a 'bacterial-like' initiation mechanism. Therefore, the current study concentrated on elucidating whether a 'eukaryotic-like' scanning mechanism might operate instead. GUG and UUG were efficiently used as start codons on leadered transcripts in vivo, in contrast to initiation on leaderless transcripts (and leadered eukaryotic transcripts). Deleted versions of the 5'-UTR initiated translation very inefficiently. Introduction of additional upstream AUGs did not influence the initiation efficiency at internal start codons. An additional in-frame AUG at the 5'-end led to the simultaneous usage of two start sites on the same message. A stable stem-loop structure at the 5'-end inhibited only initiation at the first AUG, but did not influence usage of the internal AUG. Taken together, operation of a scanning mechanism was excluded and the results indicate that a novel mechanism for translation initiation operates at least in haloarchaea.
authors.affiliation: Goethe-University, Department of Biosciences, Biocentre, Institute for Molecular Biosciences, Max-von-Laue-Str. 9, D-60438 Frankfurt, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Hering
authors.forename: Mariam
authors.initials: M
authors.lastname: Brenneis
authors.forename: Jürgen
authors.initials: J
authors.lastname: Beer
authors.forename: Beatrix
authors.initials: B
authors.lastname: Suess
authors.forename: Jörg
authors.initials: J
authors.lastname: Soppa
mesh_terms: D020121:5' Untranslated Regions; D018387:Codon, Initiator / Q000235:genetics*; D019766:Genes, Archaeal; D019622:Haloferax volcanii / Q000235:genetics*; D009690:Nucleic Acid Conformation; D014176:Protein Biosynthesis; D019642:RNA, Archaeal / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics
chemical_list: D020121:5' Untranslated Regions; D018387:Codon, Initiator; D019642:RNA, Archaeal; D012333:RNA, Messenger