title: The toxin GraT inhibits ribosome biogenesis.
abstract: Most bacteria encode numerous chromosomal toxin-antitoxin (TA) systems that are proposed to contribute to stress tolerance, as they are able to shift the cells to a dormant state. Toxins act on a variety of targets with the majority attacking the translational apparatus. Intriguingly, the toxicity mechanisms of even closely related toxins may differ essentially. Here, we report on a new type of TA toxin that inhibits ribosome biogenesis. GraT of the GraTA system has previously been described in Pseudomonas putida as an unusually moderate toxin at optimal growth temperatures. However, GraT causes a severe growth defect at lower temperatures. Here, we demonstrate that GraT causes the accumulation of free ribosomal subunits. Mapping the rRNA 5' ends reveals incomplete processing of the free subunits and quantification of modified nucleosides shows an underrepresentation of late subunit assembly specific modifications. This indicates that GraT inhibits ribosome subunit assembly. Interestingly, GraT effects can be alleviated by modification of the chaperone DnaK, a known facilitator of late stages in ribosome biogenesis. We show that GraT directly interacts with DnaK and suggest two possible models for the role of this interaction in GraT toxicity.
authors.affiliation: Institute of Molecular and Cell Biology, University of Tartu, 51010, Tartu, Estonia.
authors.forename: Andres
authors.initials: A
authors.lastname: Ainelo
authors.affiliation: Institute of Molecular and Cell Biology, University of Tartu, 51010, Tartu, Estonia.
authors.forename: Hedvig
authors.initials: H
authors.lastname: Tamman
authors.affiliation: Institute of Molecular and Cell Biology, University of Tartu, 51010, Tartu, Estonia.
authors.forename: Margus
authors.initials: M
authors.lastname: Leppik
authors.affiliation: Institute of Molecular and Cell Biology, University of Tartu, 51010, Tartu, Estonia.
authors.forename: Jaanus
authors.initials: J
authors.lastname: Remme
authors.affiliation: Institute of Molecular and Cell Biology, University of Tartu, 51010, Tartu, Estonia.
authors.forename: Rita
authors.initials: R
authors.lastname: Hõrak
mesh_terms: D001427:Bacterial Toxins / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D018832:Molecular Chaperones; D001678:Organelle Biogenesis; D016958:Pseudomonas putida / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D012329:RNA, Bacterial / Q000235:genetics; D012335:RNA, Ribosomal; D012270:Ribosomes / Q000235:genetics / Q000378:metabolism*
chemical_list: D001427:Bacterial Toxins; D018832:Molecular Chaperones; D012329:RNA, Bacterial; D012335:RNA, Ribosomal