The Kluyveromyces lactis gamma-toxin targets tRNA anticodons

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Jian Lu1, Bo Huang, Anders Esberg

  • 1Department of Molecular Biology, Umeå University, Sweden.

RNA (New York, N.Y.)
|October 26, 2005
PubMed

Insights

Kluyveromyces lactis killer strains produce zymocin, a toxin that halts yeast growth. This study identifies three specific transfer RNA (tRNA) molecules as the targets of zymocin, revealing its mechanism of action.

Area of Science:

  • Molecular Biology
  • Yeast Genetics
  • Toxinology

Background:

  • Kluyveromyces lactis killer strains secrete zymocin, a toxin causing irreversible yeast growth arrest.
  • The specific molecular target of zymocin's cytotoxic gamma-subunit has been a long-standing mystery in yeast research.

Purpose of the Study:

  • To identify the elusive molecular target(s) of the zymocin gamma-subunit.
  • To elucidate the mechanism by which zymocin inhibits yeast growth at the molecular level.

Main Methods:

  • Identification of specific tRNA species targeted by the gamma-toxin.
  • Analysis of the cleavage site within the targeted tRNAs.
  • Investigation of the role of modified nucleosides in toxin susceptibility using mutant strains.

Main Results:

  • Three tRNA species—tRNA(Glu)(mcm(5)s(2)UUC), tRNA(Lys)(mcm(5)s(2)UUU), and tRNA(Gln)(mcm(5)s(2)UUG)—were identified as direct targets of the gamma-toxin.
  • The toxin functions by cleaving these tRNAs at the 3' side of the modified wobble nucleoside 5-methoxycarbonylmethyl-2-thiouridine (mcm(5)s(2)U).
  • Yeast strains deficient in the mcm(5) group modification exhibited resistance to gamma-toxin, correlating with inefficient tRNA cleavage.

Conclusions:

  • The K. lactis gamma-toxin represents the first identified eukaryotic toxin that specifically targets transfer RNA (tRNA).
  • The toxin's mechanism involves the specific cleavage of modified tRNAs, disrupting essential cellular processes.
  • Understanding this mechanism provides insights into yeast toxin resistance and tRNA modification pathways.

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