Poster abstracts

Poster number 62 submitted by Divyaa Bhagdikar

Identification and characterization of S-box riboswitches that regulate at the level of translation initiation

Divyaa Bhagdikar (Department of Microbiology and Center for RNA biology , The Ohio State University, Columbus, OH 43210 ), Frank J. Grundy (Department of Microbiology and Center for RNA biology , The Ohio State University, Columbus, OH 43210 ), Tina M. Henkin (Department of Microbiology and Center for RNA biology , The Ohio State University, Columbus, OH 43210 )

Abstract:
S-box riboswitches regulate the expression of genes involved in methionine metabolism. These riboswitches contain an aptamer domain that binds S-adenosylmethionine (SAM) and an expression platform that undergoes a SAM-dependent conformational rearrangement to regulate the expression of downstream genes. When intracellular levels of SAM are high, SAM binds to the aptamer domain, which stabilizes a terminator helix that leads to premature termination of transcription. When SAM levels are low, an alternate antiterminator helix forms that allows transcription of the downstream genes. In silico analyses have suggested that a rarer class of S-box riboswitches regulate at the level of translation initiation. We identified two leader RNAs that have the potential for SAM-dependent sequestration of the Shine-Dalgarno (SD) region of the mRNA. The aptamer domains of both of these RNAs bound SAM with affinities comparable to that of the well-characterized Bacillus subtilis yitJ S-box riboswitch, and with similar selectivity against S-adenosylhomocysteine (SAH). Mutation of a residue previously shown to be essential for SAM binding in other S-box riboswitches resulted in loss of SAM binding. These results demonstrate that the aptamer domains have SAM binding properties similar to that of previously characterized S-box riboswitches. We also demonstrated that the SD regions of both these RNAs exhibited SAM-dependent structural rearrangements consistent with the hypothesis that regulation occurs at the level of translation initiation.

Keywords: S-box, Translation, Riboswitch