Identification of host factors required for Ty1 transposition in yeast.

Abstract

Ty1 is a retrotransposon with a life cycle similar to that of retroviruses such as HIV (Human immunodeficiency Virus). HIV host cells are not very amenable to genetic analysis, crucial for the identification of host factors essential for the life cycle of HIV. Thus we have used Saccharomyces cerevisiae to identify host factors necessary for Ty1 transposition. Using yeast mutant strains each with a deletion of a non-essential nucleoporin gene to carry out the transposition assay we conclude that the nucleoporins, NUP120, NUP188, NUP84, NUP170 and SEH1 are critical for the life cycle of Ty1. Using yeast two hybrid screen with the Ty1 Gag-like protein as bait we identified 8 proteins interacting with the Ty1 Gag-like protein, GlPs (Gag Interacting Proteins). However none of the GlPs identified were critical for the transposition of Ty1 as deletion of the GIP genes did not affect the transposition efficiency. Two out of the eight GlPs identified are involved in the ubiquitinatlon pathway. Using deletion strains for the transposition assay we conclude that the protein complex ESCRT-I (VPS23, VPS28, VPS37) and VPS27 are important for the life cycle of Tyl as deletion of any of these genes reduced the transposition frequency. TSG101 (mammalian Vps23) is recruited to plasma membrane for the budding of HIV virus, suggesting that although Ty1 does not form a envelope covered virus particle it still uses the same machinery as HIV, further strengthening the close similarity between HIV and Ty1 life cycle raising the possibility that Ty1 can be used to screen for potential therapeutic drugs against retroviruses.