The main area of interest in our laboratory is the analysis of the mechanisms through which cells sense changes in their environment and transmit that information to the level of gene expression.We use the Gram-positive bacterium Bacillus subtilis as a model system, and we focus primarily on genes involved in protein synthesis and amino acid metabolism.We have uncovered systems in which nascent RNA transcripts act as riboswitches to directly sense physiological signals and control gene expression through RNA structural rearrangements.
Nascent RNAs can sense uncharged tRNA: the T box riboswitch
Characterization of the B. subtilis tyrS gene, encoding tyrosyl-tRNA synthetase, revealed a novel mechanism of gene regulation at the level of transcription antitermination. The tyrSgene is a member of a large family of aminoacyl-tRNA synthetase and amino acid biosynthesis genes in Gram-positive bacteria that are regulated by a common mechanism.Each gene in this family responds individually to limitation for the appropriate amino acid. Amino acid limitation is monitored via interaction of the 5’ region of the nascent transcript with the cognate uncharged tRNA.This interaction is directed by pairing of the anticodon of the tRNA with a single codon, designated the "Specifier Sequence," in the mRNA.The mRNA-tRNA interaction occurs in the absence of translation, and antitermination can occur in a purified transcription system with no additional cellular factors, indicating that the mRNA is sufficient for specific recognition of the cognate tRNA.We are currently investigating the molecular details of the leader RNA-tRNA interaction, and the structural shifts in both RNA partners that occur upon binding.We are also testing novel antibiotics for their ability to target the T box mechanism.
Nascent RNAs can sense small molecules: metabolite-binding riboswitch RNAs
Analysis of genes involved in methionine metabolism revealed a second global transcription antitermination system, dedicated to genes in this pathway.Like the T box system, the S box system is widely used in Gram-positive organisms. Genes regulated by this mechanism contain highly conserved sequence and structural elements in their mRNAs, and expression is induced by starvation for methionine. We have now shown that the molecular effector for this system is S–adenosylmethionine (SAM), which binds directly to the leader RNA and modulates its structure to promote transcription termination. A second SAM-binding RNA, the SMK box, was identified in lactic acid bacteria and shown to regulate gene expression at the level of translation initiation.We have also shown that lysine biosynthesis genes are regulated by a similar mechanism, with specific leader RNA binding of lysine.Current work is focusing on the molecular mechanisms of effector recognition and RNA rearrangement in response to effector binding.
Tina Henkin's Curriculum Vitae [pdf]
Member, Center for RNA Biology
- Sherwood AV, Grundy FJ & Henkin TM. (2015) T box riboswitches in Actinobacteria: translational regulation via novel tRNA interactions. Proc. Natl. Acad. Sci. USA, in press.
- Henkin TM. (2014) The T box riboswitch: a novel regulatory RNA that utilizes tRNA as its ligand. Biochim. Biophys. Acta, Gene Regulatory Mechanisms. Special Issue: Riboswitches 1839:959-963.
- Grigg JC, Chen Y, Grundy FJ, Henkin TM, Pollack L & Ke A. (2013) T box RNA decodes both the information content and geometry of tRNA to affect gene expression. Proc. Natl. Acad. Sci. USA. 110:7240-7245.
- Caserta E, Haemig H, Manias D, Tomsic J, Grundy FJ, Henkin TM & Dunny G. (2012) In vivo and in vitro analysis of regulation of the pheromone-responsive prgQ promoter by the PrgX pheromone receptor protein. J. Bacteriol. 194:3386-3394.
- Wilson-Mitchell SN, Grundy FJ & Henkin TM. (2012) Analysis of Lysine recognition and specificity of the Bacillus subtilis L box riboswitch. Nucl. Acids Res.. 40:5706-5717
- Lu C, Smith AM, Ding F, Chowdhury A, Henkin TM & Ke A. (2011) Variable sequences outside the SAM-binding core critically influence the conformational dynamics of the SAM-III/SMK box riboswitch. J. Mol. Biol. 409, 786-799.
- Wilson RC, Smith AM, Fuchs RT, Kleckner IR, Henkin TM & Foster MP. (2011) Tuning riboswitch regulation through conformational selection. J Mol Biol. 405, 926-938.
- Smith AM, Fuchs RT, Grundy FJ & Henkin TM. (2010) The SMK box of Enterococcus faecalis is a reversible riboswitch. Mol Microbiol. 78,1393-1402.
- Lu C, Ding F, Chowdhury A, Pradhan V, Tomsic J, Holmes MW, Henkin TM & Ke A. (2010) SAM recognition and conformational switching mechanism in the Bacillus subtilis yitJ S Box/SAM-I riboswitch. J Mol Biol. 404, 803-818.
- Wang J, Henkin TM & Nikonowicz EP. (2010) NMR structure and dynamics of the Specifier Loop domain from the Bacillus subtilis tyrS T box leader RNA. Nucl. Acids Res. 38, 3388-3398.
- Smith AM, Fuchs RT & Henkin TM. (2010) Riboswitch RNAs: Regulation of gene expression by direct monitoring of a physiological signal. RNA Biol. 7, 104-110.
- Johnson CM, Manias DA, Haemig HA, Shokeen S, Weaver KE, Henkin TM & Dunny GA. (2010) Direct evidence for control of the pheromone prgQ operon of Enterococcus faecalis plasmid pCF10 by a countertranscript-driven attenuation mechanism. J Bacteriol. 192, 1634-1642.
- Green NR, Grundy FJ & Henkin TM. (2010) The T box mechanism: tRNA as a regulatory molecule. FEBS Lett. 584,318-24.
Snyder LR, Peters JE, Henkin TM & Champness WC. (2012) Molecular Genetics of Bacteria, 4th Edition. American Society for Microbiology, Washington, DC, in press.
The all-time favorite
- Grundy FJ & Henkin TM. (1993) tRNA as a positive regulator of transcription antitermination in B. subtilis. Cell. 74, 475-82.
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