Poster abstracts

Poster number 41 submitted by Sean McClory

Mutations in 16S rRNA that confer defects in decoding

Sean McClory (Department of Microbiology, The Ohio State University), Daoming Qin (Department of Microbiology, The Ohio State University), Josh Leisring (Department of Microbiology, The Ohio State University), Kurt Fredrick (Department of Microbiology, The Ohio State University)

Abstract:
Accurate translation of the genetic code by the ribosome requires the discrimination of cognate aminoacyl (aa)-tRNA from near-cognate aa-tRNAs that differ by only a single anticodon nucleotide. Structural and kinetic data suggest that a conformational change in the ribosome upon binding of aa-tRNA is critical for translational fidelity, but important details of this mechanism remain unclear. Ribosomal ambiguity (ram) mutations, which confer decoding defects, have provided important clues to this mechanism, although they have previously been isolated almost entirely in ribosomal proteins. In this study, we have employed a specialized ribosome system to screen for ram mutations in the 16S ribosomal RNA (rRNA). We identified 31 mutations that induce misreading of a lacZ reporter gene. These primarily map to three distinct areas: 1) the ribosomal A site where codon-anticodon pairing occurs, 2) near proteins S4 and S5 where several ram mutations have previously been mapped, and 3) in helices 8 and 14 that form a tertiary contact near the binding site of elongation factor Tu (EF-Tu) which delivers the incoming aa-tRNA to the ribosome. Recent structural studies have revealed a contact between helix 14 and the switch 1 region of EF-Tu, suggesting that the 16S may play a role in aa-tRNA selection by a direct interaction with the factor. Further analysis of these mutations may provide important details as to how the ribosome maintains the fidelity of the genetic code.

Keywords: ribosome, RNA, genetic code