Cleavage Of tRNAs Research Articles

Zymocin, a composite chitinase and tRNase killer toxin from yeast

Growth inhibition of Saccharomyces cerevisiae by the plasmid-encoded trimeric (alphabetagamma) zymocin toxin from dairy yeast, Kluyveromyces lactis, depends on a multistep response pathway in budding yeast. Following early processes that mediate cell-surface contact by the chitinase alpha-subunit of zymocin, later steps enable import of the gamma-toxin tRNase subunit and cleavage of target tRNAs that carry modified U34 (wobble uridine) bases. With the emergence of zymocin-like toxins, continued zymocin research is expected to yield new insights into the evolution of yeast pathosystems and their lethal modes of action.

Starvation-induced Cleavage of the tRNA Anticodon Loop in Tetrahymena thermophila

Amino acid deprivation triggers dramatic physiological responses in all organisms, altering both the synthesis and destruction of RNA and protein. Here we describe, using the ciliate Tetrahymena thermophila, a previously unidentified response to amino acid deprivation in which mature transfer RNA (tRNA) is cleaved in the anticodon loop. We observed that anticodon loop cleavage affects a small fraction of most or all tRNA sequences. Accumulation of cleaved tRNA is temporally coordinated with the morphological and metabolic changes of adaptation to starvation. The starvation-induced endonucleolytic cleavage activity targets tRNAs that have undergone maturation by 5' and 3' end processing and base modification. Curiously, the majority of cleaved tRNAs lack the 3' terminal CCA nucleotides required for aminoacylation. Starvation-induced tRNA cleavage is inhibited in the presence of essential amino acids, independent of the persistence of other starvation-induced responses. Our findings suggest that anticodon loop cleavage may reduce the accumulation of uncharged tRNAs as part of a specific response induced by amino acid starvation.

MRNA expression in mitochondria of the red alga Chondrus crispus requires a unique RNA-processing mechanism, internal cleavage of upstream tRNAs at pyrimidine 48

The hypothesis that tRNAs are involved in the maturation of the large primary transcripts of Chondrus crispus mitochondrial DNA was addressed by primer extension mapping of the transcript 5′ ends of the ten genes that are preceded by tRNA genes in C. crispus mitochondrial genome. Among the 12 tRNAs that were candidates as maturation signals, eight, namely tRNAArg, tRNALys, tRNAAsp, tRNAGln, tRNATrp, tRNAIle, tRNAPhe and tRNAGly, were cleaved internally upon maturation of C. crispus mitochondrial primary transcripts, all of them at the same base, invariant pyrimidine 48. Only four tRNAs departed from this pattern: tRNALeu and tRNACys, which are not maturation signals, tRNAMet, which appears to be excised as a whole from the orf94 primary trancript and tRNAAla, which is cleaved internally at positions other than Y48. Sequence comparisons between the cleaved and the uncleaved tRNAs suggest that their core tertiary structure is involved with their recognition and cleavage. However, the precursor transcripts are also processed at the 5′ and 3′ ends of the tRNAs to yield tRNA molecules that are stable and functional in translation. This indicates that two different RNA processing mechanisms coexist in C. crispus mitochondria, one required for the production of functional tRNAs and the other for the processing of mRNAs.

A cytotoxic ribonuclease targeting specific transfer RNA anticodons.

The carboxyl-terminal domain of colicin E5 was shown to inhibit protein synthesis of Escherichia coli. Its target, as revealed through in vivo and in vitro experiments, was not ribosomes as in the case of E3, but the transfer RNAs (tRNAs) for Tyr, His, Asn, and Asp, which contain a modified base, queuine, at the wobble position of each anticodon. The E5 carboxyl-terminal domain hydrolyzed these tRNAs just on the 3' side of this nucleotide. Tight correlation was observed between the toxicity of E5 and the cleavage of intracellular tRNAs of this group, implying that these tRNAs are the primary targets of colicin E5.

Recombinant photoreactive tRNA molecules as probes for cross-linking studies

Photoreactive tRNA derivatives have been used extensively for investigating the interaction of tRNA molecules with their ligands and substrates. Recombinant RNA technology facilitates the construction of such tRNA probes through site-specific incorporation of photoreactive nucleosides. The general strategy involves preparation of suitable tRNA fragments and their ligation either to a photoreactive nucleotide or to each other. tRNA fragments can be prepared by site-specific cleavage of native tRNAs, or synthesized by enzymatic and chemical means. A number of photoreactive nucleosides suitable for incorporation into tRNA are presently available. Joining of tRNA fragments is accomplished either by RNA ligase or by DNA ligase in the presence of a DNA splint. The application of this methodology to the study of tRNA binding sites on the ribosome is discussed, and a model of the tRNA-ribosome complex is presented.

Degradation of nucleic acids with ozone. IV. Specific internucleotidic bond-cleavage of ozone-treated transfer ribonucleic acids with aniline-acetate.

The treatment of transfer ribonucleic acids (tRNAs) with ozone and subsequent treatment with aniline-acetate (pH 4.5) resulted in the internucleotidic bond cleavage of tRNAs. Sequence analysis of the fragments obtained showed that the internucleotidic bond-cleavage occurred at the guanine residues modified with ozone, and the most susceptible sites were those in consecutive sequences of guanine residues, such as -GpGpGpGp- and -GpGpm1Gp-in tRNAPro.