PgmNr Y3036: S. cerevisiae RTT105 mediates Ty1 Gag localization under stress.

Authors:
J. Keeney; J. Scales


Institutes
Juniata College, Huntingdon, PA.


Keyword: Mitochondria/Vacuoles/Peroxisomes

Abstract:

The mRNA of LTR-retrotransposons encodes the replication proteins (gag and pol) and serves as the genomic material for virus-like particles (VLPs), a cytosolic structure in which the element’s genome is reverse transcribed. In the genome of Baker's yeast (Saccharomyces cerevisiae), there are several families of such retrotransposons, including the abundant Ty1 element. In S. cerevisiae, genome-wide screens have identified numerous candidate genes that mediate Ty1 transposition activity. One of these candidates, RTT105, has previously been identified as a negative regulator of native Ty1 mobility in a genetic screen. Here, we show RTT105 as a positive regulator of galactose-induced Ty1 mobility. RTT105 is uncharacterized and contains no conserved domains of known function, thus the nature of the role of RTT105 in Ty1 transposition activity remains unknown. We identified that the rtt105 mutation does not interrupt Ty1 Gag protein processing nor cDNA synthesis within mature VLPs. In permissive conditions, Rtt105p localizes at discrete cytoplasmic Ty1 Gag foci, indicating a role in VLP assembly and maturation. Ty1 RNA has been shown to localize to the ER membrane in association with the signal recognition particle (SRP), facilitating virus-like particle assembly.  In RNA-Seq analysis with isogenic rtt105 deletion and wild type strains, we found a slight down-regulation of several subunits of the signal recognition particle (SRP) complex and a significant downregulation of the RNA subunit, scR1. Further, growth in stressful environmental conditions, such as the presence of galactose or glucose deprivation, triggers Ty1 Gag protein localization to the vacuole. Interestingly, an rtt105 mutation inhibits movement of cytoplasmic Ty1 Gag protein to the vacuole in the presence of these stressors. Gag localization to the cytoplasm is reduced in an rtt105 mutant as assayed by growth of strains containing a Gag::URA3 fusion construct on 5-FOA. These results illuminate an important step in the processing and regulation of retrotransposons and suggest an additional route by which the host cell actively maintains Ty1 mobility in variable environmental conditions.



Yeast Database Genetic Index
1. gene symbol: RTT105; systematic name: YER104W