Talk abstracts

Talk on Friday 07:10-07:30pm submitted by Rebecca Hurto

Novel Connection Between Inorganic Phosphate Availability and tRNA Nucleus-cytosol Dynamics

Rebecca Hurto (Molecular Genetics, OSU), Amy Tong (Medical Research, Banting and Best, U. of Toronto), Charlie Boone (Medical Research, Banting and Best, U. of Toronto), Anita K Hopper (Molecular Genetics, OSU)

Abstract:
There are at least two routes for tRNA nuclear export in S. cerevisiae, but only the Los1p-dependent pathway is well described. Los1p, an unessential b-importin, binds tRNA in a RanGTP-dependent manner and exports tRNA out of the nucleus. We applied synthetic genetic array technology (Tong et al., 2001) to conduct a systematic, genome-scale search of unessential genes that function in Los1p-independent tRNA nuclear export. In addition to ARC1, a known interactor (Simos et al., 1996), >130 novel candidates were uncovered. As assessed by tetrad analysis and spot assay, 8 of 97 candidates have bonafide synthetic interactions. Three verified interactors, pho88-delta, gtr1-delta, and gtr2-delta, which cause tRNA nuclear accumulation, implicate inorganic phosphate (Pi) up-take in tRNA nucleus-cytosol distribution.

Synthetic sick or lethal interactions were expected to occur between los1-delta and mutants of the Los1-independent tRNA nuclear export pathway. However, pho88-delta cells accumulated cytoplasmic tRNA in their nuclei, which indicates that the synthetic interaction is due to induction of retrograde nuclear import of cytoplasmic tRNA and/or impaired re-export of tRNA to the cytosol.

Phosphate-uptake defects were phenocopied by growing wild-type cells in medium lacking Pi (SC -Pi) to take advantage of controlled starvation. Wild-type cells grown at 23 degrees C, in SC -Pi for 1 to 2 hours accumulated cytoplasmic tRNA within nuclei. This accumulation also occurred through induction of retrograde nuclear import of cytoplasmic tRNA and/or impaired re-export of tRNA to the cytosol. Whereas amino acid starvation has been shown to cause tRNA nuclear accumulation (Shaheen and Hopper, 2005), this is the first connection between Pi availability and tRNA nuclear-cytosol distribution.

Keywords: tRNA, transport