Poster abstracts

Poster number 119 submitted by Fawwaz Naeem

Sequestration of the anti-Shine-Dalgarno (ASD) causes reduced efficiency of prfB programmed frameshifting in Flavobacterium johnsoniae

Fawwaz Naeem (Ohio State Biochemistry Program, The Ohio State University), Zakkary A. McNutt (Ohio State Biochemistry Program, The Ohio State University), Kurt Fredrick (Microbiology Department, The Ohio State University)

In bacteria, two release factors are responsible for translation termination—RF1 and RF2. Production of RF2 is autoregulated in most bacteria (> 80%) via programmed frameshifting. In short, this entails a competition between RF2-dependent termination at an in-frame UGA codon and +1 frameshifting of peptidyl-tRNALeu on the slippery sequence CUUU. The frameshifting event is promoted by a SD-like sequence closely juxtaposed to the slippery sequence. Ribosomes of Bacteroidia fail to recognize SD sequences due to sequestration of the 3’ tail of the 16S rRNA on the 30S platform. Yet, in these organisms, the prfB gene typically contains the frameshift site with its characteristic SD-like sequence. Here we investigate prfB autoregulation in Flavobacterium johnsoniae, a member of the Bacteroidia. We show that the efficiency of prfB frameshifting in F. johnsoniae is low (5-6%) relative to that in E. coli (~50%). Mutation or truncation of bS21 in F. johnsoniae increases frameshifting substantially, suggesting that ASD sequestration is responsible for the reduced efficiency. The frameshift site of certain Flavobacteriales, such as Winogradskyella psychrotolerans, has lost the SD-like sequence. In F. johnsoniae, this W. psychrotolerans sequence supports frameshifting at 3-5%, which is unaffected by mutation of bS21. Collectively, these data suggest that prfB frameshifting is largely independent of SD-ASD pairing in the Bacteroidia and consequently tuned down.

Keywords: Flavobacterium johnsoniae , Ribosome, prfB frameshifting