RNA repair: An antidote to cytotoxic eukaryal RNA damage

Abstract

Breaks that occur during tRNA and mRNA processing and during cellular stress are repaired by either of two mechanisms: the yeast-type, which occurs in fungi and plants, or the phage-type pathways. The pathways function both in repairing the breaks produced by a site-specific endonuclease (healing) and in joining or sealing the ends to re-form the 3'-5'-phosphodi-ester bond. Repair and sealing in the yeast-type pathway is catalyzed by Trll, a multifunctional tRNA ligase from Saccharomyces cerevisiae, whereas for bacteriophage repair and sealing are catalyzed by the T4 enzymes polynucleotide kinase-phosphatase (Pnkp) and RNA ligase 1 (Rnll). The specificity by which these two repair mechanisms target damaged RNA and prevent nonspecific ligation of other RNAs is unknown. In addition, bacteria and fungi also secrete endoribonuclease toxins, or ribotox-ins, which are taken up by "foreign" cells and which kill or arrest the growth of the target cells due to inability to repair toxin-induced damage to essential RNAs such as tRNA. Ribotoxins thus constitute a defense or innate immune mechanism of bacteria against phage and of fungi against their pathogens. © 2008 Data Trace Publishing Company.