Arabidopsis Encodes Four tRNase Z Enzymes

Abstract

Functional transfer RNA (tRNA) molecules are a prerequisite for protein biosynthesis. Several processing steps are required to generate the mature functional tRNA from precursor molecules. Two of the early processing steps involve cleavage at the tRNA 5# end and the tRNA 3# end. While processing at the tRNA 5# end is performed by RNase P, cleavage at the 3# end is catalyzed by the endonuclease tRNase Z. In eukaryotes, tRNase Z enzymes are found in two versions: a short form of about 250 to 300 amino acids and a long form of about 700 to 900 amino acids. All eukaryotic genomes analyzed to date encode at least one long tRNase Z protein. Of those, Arabidopsis (Arabidopsis thaliana) is the only organism that encodes four tRNase Z proteins, two short forms and two long forms. We show here that the four proteins are distributed to different subcellular compartments in the plant cell: the nucleus, the cytoplasm, the mitochondrion, and the chloroplast. One tRNase Z is present only in the cytoplasm, one protein is found exclusively in mitochondria, while the third one has dual locations: nucleus and mitochondria. None of these three tRNase Z proteins is essential. The fourth tRNase Z protein is present in chloroplasts, and deletion of its gene results in an embryo-lethal phenotype. In vitro analysis with the recombinant proteins showed that all four tRNase Z enzymes have tRNA 3# processing activity. In addition, the mitochondrial tRNase Z proteins cleave tRNA-like elements that serve as processing signals in mitochondrial mRNA maturation.

RNase ZS1 processes UbL40 mRNAs and controls thermosensitive genic male sterility in rice

“…In Arabidopsis, four RNase Z proteins can process tRNA in vitro 25 : Trz1 and Trz2 (RNase Z L ) localize in the nucleus and mitochondria and may process tRNAs; Trz3 and Trz4 (RNase Z S ) localize in the chloroplasts and cytoplasm, respectively. Loss-of-function of Trz4 leads to embryo lethality, and the function of Trz3, which localizes in the cytoplasm, is largely unknown 25 . The rice genome encodes three RNase Z proteins, including one long form and two short forms (RNase Z S1 and RNase Z S2 ; Supplementary Fig.…”

“…RNase Z proteins process the 3 0 ends of tRNAs 21,[23][24][25] . The CCA sequence in 3 0 terminal of the tRNA is critical for tRNA maturation and function.…”

Partitioning of the Nuclear and Mitochondrial tRNA 3′-End Processing Activities between Two different Proteins in Schizosaccharomyces pombe

“…In addition, a role for ELAC2 in mitochondrial pre-tRNA 3Ј-end processing has recently been demonstrated in vivo (30,32). Although tRNase Z L s from some species, including S. cerevisiae (37), S. pombe (38), and A. thaliana (34), have been shown to possess tRNA 3Ј-end processing activity in vitro, their nuclear and mitochondrial tRNA 3Ј-end processing activity in vivo remains to be experimentally demonstrated.…”

“…In plants, the situation is more complex. For example, Arabidopsis thaliana has two tRNase Z L s and two tRNase Z S s. The two long forms of tRNase Z are found in both the nucleus and mitochondria and in the mitochondria, respectively, whereas the two short forms are present in the cytoplasm and chloroplasts, respectively (34).…”

P-class pentatricopeptide repeat proteins are required for efficient 5′ end formation of plant mitochondrial transcripts

“…Thus, depending on the location of these tRNA-like structures relative to the cotranscribed mRNA, processing of the t-elements contributes to 5' and/or 3' end formation of mitochondrial mRNAs in vivo, which was confirmed for 3' end formation of the nad6 mRNA by PRORP. [10][11][12] Up to now, no evidence has been found for the presence of a 5' to 3' exonucleolytic activity in plant mitochondria, suggesting that an involvement of such an activity in 5' processing is rather unlikely. 4 In contrast to the variability at the 5' ends, more or less no variation has been observed at the 3' termini of plant mitochondrial transcripts.…”