title: Structural insights into +1 frameshifting promoted by expanded or modification-deficient anticodon stem loops.
abstract: Maintenance of the correct reading frame on the ribosome is essential for accurate protein synthesis. Here, we report structures of the 70S ribosome bound to frameshift suppressor tRNA(SufA6) and N1-methylguanosine at position 37 (m(1)G37) modification-deficient anticodon stem loop(Pro), both of which cause the ribosome to decode 4 rather than 3 nucleotides, resulting in a +1 reading frame. Our results reveal that decoding at +1 suppressible codons causes suppressor tRNA(SufA6) to undergo a rearrangement of its 5' stem that destabilizes U32, thereby disrupting the conserved U32-A38 base pair. Unexpectedly, the removal of the m(1)G37 modification of tRNA(Pro) also disrupts U32-A38 pairing in a structurally analogous manner. The lack of U32-A38 pairing provides a structural correlation between the transition from canonical translation and a +1 reading of the mRNA. Our structures clarify the molecular mechanism behind suppressor tRNA-induced +1 frameshifting and advance our understanding of the role played by the ribosome in maintaining the correct translational reading frame.
authors.affiliation: Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Maehigashi
authors.affiliation: Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322.
authors.forename: Jack A
authors.initials: JA
authors.lastname: Dunkle
authors.affiliation: Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322.
authors.forename: Stacey J
authors.initials: SJ
authors.lastname: Miles
authors.affiliation: Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322 christine.m.dunham@emory.edu.
authors.forename: Christine M
authors.initials: CM
authors.lastname: Dunham
mesh_terms: D000926:Anticodon / Q000737:chemistry / Q000235:genetics; D018360:Crystallography, X-Ray; D004926:Escherichia coli / Q000235:genetics*; D018965:Frameshifting, Ribosomal / Q000235:genetics*; D016153:Genes, Suppressor; D055029:Inverted Repeat Sequences / Q000235:genetics; D009690:Nucleic Acid Conformation; D012333:RNA, Messenger / Q000737:chemistry / Q000235:genetics; D012343:RNA, Transfer / Q000737:chemistry / Q000235:genetics*; D012270:Ribosomes / Q000737:chemistry / Q000235:genetics*; D012486:Salmonella typhimurium / Q000235:genetics*; D016963:Thermus thermophilus / Q000235:genetics*
chemical_list: D000926:Anticodon; D012333:RNA, Messenger; D012343:RNA, Transfer
keywords: near cognate; processivity