title: Sustained translational repression of lactate dehydrogenase 1 in Toxoplasma gondii bradyzoites is conferred by a small regulatory RNA hairpin.
abstract: In response to environmental stresses, Toxoplasma gondii induces a global translational repression which allows for the remodeling of its transcriptome. While some transcripts are preferentially translated, another subset is translationally repressed and maintained in bradyzoites. Although little is known of how transcripts are targeted for sustained translational repression, the targeting probably operates through an RNA-centric mechanism relying on the recognition of cis-acting elements. In this study, we sought to determine if the targeting of transcripts through recognizable cis-acting elements could be responsible for the transcript-specific sustained translational repression displayed by Toxoplasma bradyzoites. We examined the UTRs of a translationally repressed gene, lactate dehydrogenase 1, and found a 40 nucleotide regulatory element in its 5'UTR. This element specifically induces translational repression in otherwise constitutively expressed transcripts. Mutational studies revealed that the formation of a small 16 nucleotide regulatory RNA hairpin is essential for this activity. We suggest that this hairpin may act as the nucleation site for the binding of an as yet to be identified trans-acting factor that allows for the transcript to be targeted for translational repression removal from the active translational pool. To our knowledge, this is the first report characterizing a specific cis-acting element contributing to post-transcriptional gene regulation in Toxoplasma and suggests the presence of a pathway by which the parasites can recognize, identify and specifically target transcripts for sustained translational repression under stressful conditions.
authors.affiliation: Department of Chemistry and Biochemistry, University of Windsor, Canada.
authors.forename: Michael
authors.initials: M
authors.lastname: Holmes
authors.forename: Vaunell
authors.initials: V
authors.lastname: Itaas
authors.forename: Sirinart
authors.initials: S
authors.lastname: Ananvoranich
mesh_terms: D020121:5' Untranslated Regions; D001483:Base Sequence; D002478:Cells, Cultured; D004794:Enzyme Repression; D006801:Humans; D055029:Inverted Repeat Sequences; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis; D015800:Protozoan Proteins / Q000235:genetics* / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics*; D017422:Sequence Analysis, DNA; D014122:Toxoplasma / Q000201:enzymology* / Q000235:genetics
chemical_list: D020121:5' Untranslated Regions; D007527:Isoenzymes; D015800:Protozoan Proteins; D034741:RNA, Small Interfering; D007770:L-Lactate Dehydrogenase; C409667:lactate dehydrogenase 1
keywords: 5′UTR; RNA hairpin; Toxoplasma gondii; lactate dehydrogenase; translational repression