Poster abstracts
Poster number 50 submitted by Mike Allen
An investigation into the regulation of metK (SAM synthetase): an atypical S-box family member
George Allen (Department of Microbiology, Center for RNA Biology), Vineeta Pradhan (Department of Microbiology, Center for RNA Biology), Frank Grundy (Department of Microbiology, Center for RNA Biology), Tina Henkin (Department of Microbiology, Center for RNA Biology)
Abstract:
S box (SAM-I) riboswitches are S-adenosylmethionine (SAM)-responsive RNA regulatory elements located at the 5’ untranslated regions of genes involved in the biosynthesis and transport of methionine and SAM (1). Binding of SAM to the riboswitch results in repression of downstream gene expression primarily via transcriptional attenuation (1). The Bacillus subtilis metK gene, which encodes SAM synthetase, is an atypical member of the S box regulon. Unlike the other 10 S box regulated transcriptional units in B. subtilis, which are induced under methionine starvation conditions that result in low SAM levels, metK is expressed only when methionine concentrations are high and SAM concentrations are low (2). The metK leader region contains additional conserved sequence elements 5’ and 3’ of the S box riboswitch, designated the Upstream (US) and Downstream (DS) boxes, respectively. These sequences are highly conserved in Bacillales sp., which include many pathogenic organisms. The US and DS box elements were shown to base-pair in the absence of SAM (2). Extensive site-directed mutagenesis revealed a core region within the US and DS box elements that are sensitive to alterations in both sequence and base-pairing potential. Additionally, mutations in these sequences result in reduced transcript stability when methionine concentrations are high and SAM concentrations are low in vivo (2). We hypothesize that an unknown trans-acting factor binds to the paired US and DS boxes when SAM is low and methionine is high to increase transcript stability. A genetic selection and screen is being employed to identify mutations in a putative trans-acting factor that decrease metK expression.
References:
1. Tomsic, J., McDaniel, B. A., Grundy, F. J. & Henkin, T. M. Natural variability in S-adenosylmethionine (SAM)-dependent riboswitches: S-box elements in Bacillus subtilis exhibit differential sensitivity to SAM In vivo and in vitro. Journal of Bacteriology 190, 823–33 (2008).
2. Pradhan, V. Characterization of the metK and yitJ leader RNAs from the Bacillus subtilis S box regulon. Ph.D. thesis, The Ohio State University (2012).
Keywords: Riboswitch, S-adenosylmethionine