Abstract
The Saccharomyces cerevisiae retrovirus-like element Ty3 inserts specifically into the initiation sites of genes transcribed by RNA polymerase III (pol III). A strain with a disruption of LHP1, which encodes the homologue of autoantigen La protein, was recovered in a screen for mutants defective in Ty3 transposition. Transposition into a target composed of divergent tRNA genes was decreased eightfold. In lhp1 mutants, Ty3 polyproteins were produced at wild-type levels, assembled into virus-like particles (VLPs) and processed efficiently. The amount of cDNA associated with these particles was about half the amount in a wild-type control at early times, but approached the wild-type level after 48 h of induction. Ty3 integration was examined at two genomic tRNA gene families and two plasmid-borne tRNA promoters. Integration was significantly decreased at one of the tRNA gene families, but was only slightly decreased at the second tRNA gene family. These findings suggest that Lhp1p contributes to Ty3 cDNA synthesis, but might also act at a target-specific step, such as integration.
Highlights
The current study was undertaken in order to identify host factors that participate in the life cycles of yeast retrotransposons
We found that disruption of LHP1 decreased Ty3 transposition into a plasmid-borne, divergent tRNA gene target and differentially affected transposition at two chromosomal tRNA gene families
We propose that Lhp1 may have two functions in Ty3 transposition: one in cDNA production and one at the target site
Summary
The current study was undertaken in order to identify host factors that participate in the life cycles of yeast retrotransposons. Ty3 is one of five retrotransposons found in Saccharomyces cerevisiae (reviewed by Boeke and Stoye, 1997; Sandmeyer et al, 2001). Ty3 is a 5.4kbp DNA sequence composed of an internal domain flanked by long-terminal repeats (LTRs) of 340bp (Clark et al, 1988). The element encodes Gag3p and Gag3–Pol3p polyproteins that are processed into mature proteins by the Ty3 protease (PR) (Hansen et al, 1992; Kirchner and Sandmeyer, 1993). Gag3p is processed into major structural proteins, capsid (CA) and nucleocapsid (NC). POL3 is expressed as a Gag3p–Pol3p fusion dependent upon a
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