title: Characterization of the reactivity determinants of a novel hairpin substrate of yeast RNase III.
abstract: RNase III enzymes form a conserved family of proteins that specifically cleave double-stranded (dsRNA). These proteins are involved in a variety of cellular functions, including the processing of many non-coding RNAs, mRNA decay, and RNA interference. Yeast RNase III (Rnt1p) selects its substrate by recognizing the structure generated by a conserved NGNN tetraloop (G2-loop). Mutations of the invariant guanosine stringently inhibit binding and cleavage of all known Rnt1p substrates. Surprisingly, we have found that the 5' end of small nucleolar RNA 48 is processed by Rnt1p in the absence of a G2-loop. Instead, biochemical and structural analyses revealed that cleavage, in this case, is directed by a hairpin capped with an AAGU tetraloop, with a preferred adenosine in the first position (A1-loop). Chemical probing indicated that A1-loops adopt a distinct structure that varies at the 3' end where Rnt1p interacts with G2-loops. Consistently, chemical footprinting and chemical interference assays indicate that Rnt1p binds to G2 and A1-loops using different sets of nucleotides. Also, cleavage and binding assays showed that the N-terminal domain of Rnt1p aids selection of A1-capped hairpins. Together, the results suggest that Rnt1p recognizes at least two distinct classes of tetraloops using flexible protein RNA interactions. This underscores the capacity of double-stranded RNA binding proteins to use several recognition motifs for substrate identification.
authors.affiliation: Groupe ARN/RNA Group, Département de Microbiologie et d'Infectiologie, Faculté de Médecine, Université de Sherbrooke, Sherbrooke, Québec, Canada J1H 5N4.
authors.forename: Ghada
authors.initials: G
authors.lastname: Ghazal
authors.forename: Sherif Abou
authors.initials: SA
authors.lastname: Elela
mesh_terms: D001483:Base Sequence; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D009690:Nucleic Acid Conformation; D012315:RNA Caps / Q000737:chemistry; D012330:RNA, Double-Stranded / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D043244:Ribonuclease III / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D012315:RNA Caps; D012330:RNA, Double-Stranded; D029701:Saccharomyces cerevisiae Proteins; C468367:RNT1 protein, S cerevisiae; D043244:Ribonuclease III