Article

Identification of a Human Endonuclease Complex Reveals a Link between tRNA Splicing and Pre-mRNA 3′ End Formation

PTC Therapeutics, 100 Corporate Court, South Plainfield, NJ 07080, USA.
Cell (Impact Factor: 32.24). 05/2004; 117(3):311-21. DOI: 10.1016/S0092-8674(04)00342-3
Source: PubMed

ABSTRACT

tRNA splicing is a fundamental process required for cell growth and division. The first step in tRNA splicing is the removal of introns catalyzed in yeast by the tRNA splicing endonuclease. The enzyme responsible for intron removal in mammalian cells is unknown. We present the identification and characterization of the human tRNA splicing endonuclease. This enzyme consists of HsSen2, HsSen34, HsSen15, and HsSen54, homologs of the yeast tRNA endonuclease subunits. Additionally, we identified an alternatively spliced isoform of SEN2 that is part of a complex with unique RNA endonuclease activity. Surprisingly, both human endonuclease complexes are associated with pre-mRNA 3' end processing factors. Furthermore, siRNA-mediated depletion of SEN2 exhibited defects in maturation of both pre-tRNA and pre-mRNA. These findings demonstrate a link between pre-tRNA splicing and pre-mRNA 3' end formation, suggesting that the endonuclease subunits function in multiple RNA-processing events.

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    • "In sum, a major discovery from this work is the possibility that three pathways operate in parallel to export introncontaining pre-tRNAs from the nucleus to the cytoplasm (Fig. 1A). Targeting tRNAs and the SEN complex to mitochondria for tRNA splicing Unlike the human SEN complex that is located in the nucleus (Paushkin et al. 2004 ), the yeast SEN complex is located on the outer surface of mitochondria (Yoshihisa et al. 2003 ). Therefore, after nuclear export, intron-containing tRNAs must locate to mitochondria. "
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    • "During their nuclear biogenesis, pre-tRNAs undergo various maturation steps including cleavage of the 5′ leader sequence by RNase P, RNase Z-dependent 3′ end processing, 3′ CCA addition and introduction of a myriad of nucleotide modifications (reviewed in Ref. [24]). Interestingly, in yeast, splicing of intron-containing tRNAs takes place on the mitochondrial outer surface [25] [26], whereas in mammalian cells, the tRNA splicing machinery is located within the nucleus [27] and intron removal takes place prior to export through the NPC. The major export receptor for tRNAs, which is specific for this class of RNAs, is Los1 in yeast (EXP-t/ XpoT in mammals) [28] [29] [30] and translocation follows the general paradigm for Ran-dependent transport (Fig. 2a). "
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    • "ELAC2 was suggested to be involved in nuclear and mitochondrial tRNA 3 ′ end processing in vivo, whereas the cellular role of ELAC1 remains unclear (Rossmanith 2011). A subset of pre-tRNAs contains introns that are removed during nuclear tRNA splicing reactions in mammals (Paushkin et al. 2004). Prior to export to the cytoplasm, the nucleotidyltransferase Trnt1 adds a nontemplated CCA trinucleotide to the 3 ′ end of the tRNA that acts as a prerequisite for aminoacylation (Reichert et al. 2001). "
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