Several RNase T2 enzymes function in induced tRNA and rRNA turnover in the ciliate Tetrahymena

Abstract

The functions of eight Tetrahymena thermophila genes encoding RNase T2 family proteins (Rnt2 proteins) are explored in strains lacking one RNT2 gene or combinations of genes. At least three Tetrahymena RNase T2 enzymes are involved in the conditionally induced turnover of tRNA and rRNA.

A Tetrahymena Piwi Bound to Mature tRNA 3′ Fragments Activates the Exonuclease Xrn2 for RNA Processing in the Nucleus

“…RNP maturation would then involve tRNA nicking and passenger-strand degradation and/or unwinding activities. The nuclease(s) responsible for trimming Twi12-bound tRNAs could be broad rather than tRNA-specific in their substrate cleavage specificity, as shown for the Tetrahymena RNase T2 enzymes involved in starvation-induced tRNA cleavages (Andersen and Collins, 2012). An N-terminally truncated form of Twi12 (Twi12 S ) shows increased retention of tRNA 5' fragments under native purification conditions (Couvillion et al, 2010; Figure 1B).…”

Evidence for autophagy-dependent pathways of rRNA turnover inArabidopsis

“…Mutant alleles of RNASET2 are associated with accumulation of undigested rRNA within lysosomes in zebrafish and human neurons, 18,66 and rRNA is a cellular substrate for the RNase T2 enzymes of unicellular eukaryotes such as yeast and Tetrahymena during nutrient starvation. 22,23 We previously showed that under normal growth conditions rns2-2 and antisense RNS2 plants had rRNA with extended half-life, indicating that rRNA is a substrate for RNS2 in plants. Labeling with the RNA-specific stain SYTO RNASelect suggested that RNA accumulated in the vacuoles of rns2-2 mutants.…”

“…For example, RNase T2 enzymes accumulate in the vacuoles of phosphatedeprived tomato cells in parallel with significant rRNA degradation; 2 Rny1, the only RNase T2 enzyme in yeast, is responsible for rRNA and bulk RNA degradation in response to starvation and oxidative stress which results in metabolic changes; 5,21,22 and mutations affecting Tetrahymena thermophila RNase T2 enzymes cause changes in the patterns of rRNA degradation observed under starvation, suggesting that these enzymes also participate in a ribophagy-like mechanism as a nutrient stress response. 23 While there is some agreement that rRNA degradation can occur in the vacuole or lysosome in plants and animals, the mechanisms of transport of rRNA or ribosomes to these organelles is not well characterized, with only the ribophagy mechanism in yeast being somewhat understood. The analysis of rns2-2 phenotypes led us to hypothesize that autophagy may be part of this process.…”

Slicing tRNAs to boost functional ncRNA diversity

“…30 For example, in Tetrahymena thermophila tRNA halves production has been detected under cold shock, but not during heat shock. 31 Importantly, human tRNAs do not respond to apoptosis-inducing agents like γ-irradiation, 28 etoposide-treatment, 25 or caffeine treatment, 25,32 indicating cell deathindependent pathways for tRNA cleavage. The best described enzymes responsible for cleavage are Rny1 33 in yeast and angiogenin 32 in higher eukaryotes ( Fig.…”