Novel yeast killer toxins provoke S‐phase arrest and DNA damage checkpoint activation^‡

Abstract

SummaryCertain strains of Pichia acaciae and Wingea robertsiae (synonym Debaryomyces robertsiae ) harbour extranuclear genetic elements that confer a killer phenotype to their host. Such killer plasmids (pPac1-2 of P. acaciae and pWR1A of W. robertsiae ) were sequenced and compared with the zymocin encoding pGKL1 of Kluyveromyces lactis . Both new elements were found to be closely related to each other, but they are only partly similar to pGKL1. As for the latter, they encode functions mediating binding of the toxin to the target cell's chitin and a hydrophobic region potentially involved in uptake of a toxin subunit by target cells. Consistently, mutations affecting the target cell's major chitin synthase (Chs3) protect it from toxin action. Heterologous intracellular expression of respective open reading frames identified cell cyclearresting toxin subunits deviating structurally from the likewise imported g g g g -subunit of the K. lactis zymocin. Accordingly, toxicity of both P. acaciae and Wingea toxins was shown to be independent of RNA polymerase II Elongator, which is indispensable for zymocin action. Thus, P. acaciae and Wingea toxins differ in their mode of action from the G1-arresting zymocin. Fluorescence-activated cell sorting analysis and determination of budding indices have proved that such novel toxins mediate cell cycle arrest post-G1 during the S phase. Concomitantly, the DNA damage checkpoint kinase Rad53 is phosphorylated. As a mutant carrying the checkpoint-deficient allele rad53-11 displays toxin hypersensitivity, damage checkpoint activation apparently contributes to coping with toxin stress, rather than being functionally implemented in toxin action.

Microbial Community Structure and Dynamics of Dark Fire-Cured Tobacco Fermentation

“…The predominance of D. hansenii in a number of fermented dairy products prevents spoilage by clostridial species through the production of antibacterial metabolites (14). In addition, D. hansenii produces a killer toxin that is active against various yeast species and molds (19,27). By analogy, the presence of D. hansenii during the early stages of tobacco fermentation might facilitate the growth of lactic acid bacteria and prevent outgrowth of molds.…”

Antifungal and antitumor models of bioactive protective peptides

“…β-1,6 Glucan, α-1,3 mannoprotein and β-1,3 glucan are possible receptors, the latter for killer toxins from species of Pichia and Williopsis. Killer toxins kill susceptible cells by various mechanisms, including the induction of cation-selective ion channels in the plasma membrane, interference in the cell cycle (G1, G1/S, S arrest), chromosomal DNA synthesis and anticodon nuclease (Schmitt and Breinig 2006, Santos and Marquina 2004, Jablonowski and Schaffrath 2007, Klassen et al 2004. Killer toxins can induce apoptosis mediated by yeast caspase Yca1p, characterized by DNA fragmentation, and phosphatidylserine external membrane expression.…”

Structure–activity relationships in Kluyveromyces lactis γ-toxin, a eukaryal tRNA anticodon nuclease

“…Kluyveromyces lactis and Pichia acaciae harbor cytoplasmic episomes, called ''killer'' plasmids, that encode secreted protein toxins known as zymocin and PaT, respectively (Stark and Boyd 1986;Klassen et al 2004;Jablonowski and Schaffrath 2007). Zymocin is a heterotrimer of a, b, and g subunits that arrests growth of the non-self-yeast species Saccharomyces cerevisiae by exposure from without.…”