Utp8p Is a Nucleolar tRNA-binding Protein That Forms a Complex with Components of the Nuclear tRNA Export Machinery inSaccharomyces cerevisiae

Abstract

Utp8p is an essential nucleolar component of the nuclear tRNA export machinery in Saccharomyces cerevisiae. It is thought to act at a step between tRNA maturation/aminoacylation and translocation of the tRNA across the nuclear pore complex. To understand the function of Utp8p in nuclear tRNA export, a comprehensive affinity purification analysis was conducted to identify proteins that interact with Utp8p in vivo. In addition to finding proteins that have been shown previously to copurify with Utp8p, a number of new interactions were identified. These interactions include aminoacyl-tRNA synthetases, the RanGTPase Gsp1p, and nuclear tRNA export receptors such as Los1p and Msn5p. Characterization of the interaction of Utp8p with a subset of the newly identified proteins suggests that Utp8p most likely transfer tRNAs to the nuclear tRNA export receptors by using a channeling mechanism.

Nsf1/Ypl230w participates in transcriptional activation during non-fermentative growth and in response to salt stress in Saccharomyces cerevisiae

“…Transformants of AVY4 with pNOP1-dsRED (Strub et al, 2007) were precultured to exponential phase (OD 600 0.5-0.6) in SD minus leucine media. Cells were harvested, washed and transferred to the indicated media and further incubated.…”

Powering through ribosome assembly

“…Examples of cross talk between ribosome assembly and other cellular processes mediated through shared components include replication, rRNA transcription, tRNA export, cell cycle control, and stress response (e.g., Angermayr and Bandlow 2002;Du and Stillman 2002;Steiner-Mosonyi et al 2003;Killian et al 2004;Bernstein et al 2007;Rudra et al 2007;Strub et al 2007;Jwa et al 2008), and this cross talk is more evolved in higher organisms. Because the connection to the cell cycle has been recently and expertly reviewed (Dez and Tollervey 2004;, it will not be covered here.…”

Protein Kinase A Is Part of a Mechanism That Regulates Nuclear Reimport of the Nuclear tRNA Export Receptors Los1p and Msn5p

“…The mechanism responsible for tRNA export in S. cerevisiae is complex, involving several pathways. The S. cerevisiae tRNA export process begins in the nucleolus by aminoacylation quality assurance of mature tRNAs derived from extensive processing of intronless and intron-containing precursor tRNAs (pre-tRNAs) (31)(32)(33)(34). tRNAs made from both classes of pre-tRNAs that are deemed functional by aminoacylation are collected from the aminoacyl-tRNA synthetases in the nucleolus by Utp8p and delivered to the nuclear tRNA export receptors Los1p and Msn5p in the nucleoplasm and at the nuclear pore complex (NPC) using a channeling mechanism (33).…”

“…The S. cerevisiae tRNA export process begins in the nucleolus by aminoacylation quality assurance of mature tRNAs derived from extensive processing of intronless and intron-containing precursor tRNAs (pre-tRNAs) (31)(32)(33)(34). tRNAs made from both classes of pre-tRNAs that are deemed functional by aminoacylation are collected from the aminoacyl-tRNA synthetases in the nucleolus by Utp8p and delivered to the nuclear tRNA export receptors Los1p and Msn5p in the nucleoplasm and at the nuclear pore complex (NPC) using a channeling mechanism (33). While Utp8p is required to deliver functional tRNAs made from both intronless and intron-containing pre-tRNAs, Utp8p depends on the function of Utp9p to deliver functional tRNAs made from intron-containing precursors to Msn5p, but not Los1p (26), and on the function of Utp22p to deliver functional tRNAs made from both classes of pre-tRNAs to Los1p, but not Msn5p (35).…”

“…While Utp8p is required to deliver functional tRNAs made from both intronless and intron-containing pre-tRNAs, Utp8p depends on the function of Utp9p to deliver functional tRNAs made from intron-containing precursors to Msn5p, but not Los1p (26), and on the function of Utp22p to deliver functional tRNAs made from both classes of pre-tRNAs to Los1p, but not Msn5p (35). In addition to delivering tRNAs to the export receptors, Utp8p facilitates formation of the Los1p export complex, consisting of Los1p, tRNA, and the Ran GTPase Gsp1p bound to GTP (33), whereas Utp8p and Utp9p are both needed to form the Msn5p-tRNA-Gsp1p-GTP export complex (26). However, Utp22p does not appear to be required for formation of the Los1p-tRNA-Gsp1p-GTP export complex (35).…”