Utp9p Facilitates Msn5p-mediated Nuclear Reexport of Retrograded tRNAs in Saccharomyces cerevisiae

Abstract

Utp9p is a nucleolar protein that is part of a subcomplex containing several U3 snoRNA-associated proteins including Utp8p, which is a protein that shuttles aminoacyl-tRNAs from the nucleolus to the nuclear tRNA export receptors Los1p and Msn5p in Saccharomyces cerevisiae. Here we show that Utp9p is also an intranuclear component of the Msn5p-mediated nuclear tRNA export pathway. Depletion of Utp9p caused nuclear accumulation of mature tRNAs derived from intron-containing precursors, but not tRNAs made from intronless pre-tRNAs. Utp9p binds tRNA directly and saturably, and copurifies with Utp8p, Gsp1p, and Msn5p, but not with Los1p or aminoacyl-tRNA synthetases. Utp9p interacts directly with Utp8p, Gsp1p, and Msn5p in vitro. Furthermore, Gsp1p forms a complex with Msn5p and Utp9p in a tRNA-dependent manner. However, Utp9p does not shuttle between the nucleus and the cytoplasm. Because tRNA splicing occurs in the cytoplasm and the spliced tRNAs are retrograded back to the nucleus, we propose that Utp9p facilitates nuclear reexport of retrograded tRNAs. Moreover, the data suggest that Utp9p together with Utp8p translocate aminoacyl-tRNAs from the nucleolus to Msn5p and assist with formation of the Msn5p-tRNA-Gsp1p-GTP export complex.

Plants, like mammals, but unlikeSaccharomyces,do not regulate nuclear-cytoplasmic tRNA trafficking in response to nutrient stress

“…18 In contrast to plants and mammals, S. cerevisiae regulates nuclear export of mature spliced tRNAs but not tRNAs derived from intronless precursors in response to amino acids or nitrogen availability. [18][19][20] Moreover, while the Atg8-containing autophagosomes than cells grown in complete media (Fig. 1B), as expected.…”

“…13,14,[18][19][20] Consequently, the effect of nitrogen or sucrose starvation on nuclear-cytoplasmic distribution of tRNA in Arabidopsis and BY-2 cells was investigated. Toward this end, we first verified that starvation conditions employed in this study affect plant cellular processes.…”

tRNA biology charges to the front

“…(Since los1D msn5D double mutants are hearty, there must be at least one other unidentified exporter for tRNA nuclear export in yeast.) Second, as described further below, Msn5 functions in the tRNA reexport part of the retrograde process (Eswara et al 2009;Murthi et al 2010). Likewise, in Drosophila, where the Exportin-t ortholog is absent, the Exportin-5 ortholog dmExp5 serves as a tRNA nuclear exporter in addition to serving for pre-miRNA nuclear export (S Shibata et al 2006).…”

Transfer RNA Post-Transcriptional Processing, Turnover, and Subcellular Dynamics in the YeastSaccharomyces cerevisiae

“…Moreover, the studies have generated numerous unanticipated discoveries. It is now known that tRNAs can be aminoacylated in the nucleus (Lund and Dahlberg 1998;Sarkar et al 1999;Grosshans et al 2000a), that tRNAs can traffic from the cytoplasm to the nucleus via the tRNA retrograde process (Shaheen and Hopper 2005;Takano et al 2005;Zaitseva et al 2006), and that tRNAs imported into the nucleus can be reexported to the cytoplasm (Whitney et al 2007;Eswara et al 2009) (Figure 3). tRNA subcellular traffic is conserved (Zaitseva et al 2006;Shaheen et al 2007;Barhoom et al 2011), responsive to nutrient availability (Shaheen and Hopper 2005;Hurto et al 2007;Shaheen et al 2007;Whitney et al 2007;Murthi et al 2010), and, in yeast, is coordinated with the formation of P-bodies in the cytoplasm (Hurto and Hopper 2011).…”