Local features determine Ty3 targeting frequency at RNA polymerase III transcription start sites.

Retroelement integration into host genomes affects chromosome structure and function. A goal of a considerable number of investigations is to elucidate features influencing insertion site selection. The Ty3 retrotransposon inserts proximal to the transcription start sites (TSS) of genes transcribed by RNA polymerase III (RNAP3).

Control of yeast retrotransposons mediated through nucleoporin evolution.

Yeasts serve as hosts to several types of genetic parasites. Few studies have addressed the evolutionary trajectory of yeast genes that control the stable co-existence of these parasites with their host cell. In Saccharomyces yeasts, the retrovirus-like Ty retrotransposons must access the nucleus.

Function of a retrotransposon nucleocapsid protein.

Long terminal repeat (LTR) retrotransposons are not only the ancient predecessors of retroviruses, but they constitute significant fractions of the genomes of many eukaryotic species. Studies of their structure and function are motivated by opportunities to gain insight into common functions of retroviruses and retrotransposons, diverse mechanisms of intracellular genomic mobility, and host factors that diminish or enhance retrotransposition. This review focuses on the nucleocapsid (NC) protein of a Saccharomyces cerevisiae LTR retrotransposon, the metavirus, Ty3.

Ty3 requires yeast La homologous protein for wild-type frequencies of transposition.

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.

Mutational analysis of the transcription factor IIIB-DNA target of Ty3 retroelement integration.

The Ty3 retrovirus-like element inserts preferentially at the transcription initiation sites of genes transcribed by RNA polymerase III. The requirements for transcription factor (TF) IIIC and TFIIIB in Ty3 integration into the two initiation sites of the U6 gene carried on pU6LboxB were previously examined. Ty3 integrates at low but detectable frequencies in the presence of TFIIIB subunits Brf1 and TATA-binding protein.

Ty3 integrase is required for initiation of reverse transcription.

The integrase (IN) encoded by the Saccharomyces cerevisiae retrovirus-like element Ty3 has features found in retrovirus IN proteins including the catalytic triad, an amino-terminal zinc-binding motif, and a nuclear localization sequence. Mutations in the amino- and carboxyl-terminal domains of Ty3 IN cause reduced accumulation of full-length cDNA in the viruslike particles. We show that the reduction in cDNA is accompanied by reduced amounts of early intermediates such as minus-strand, strong-stop DNA.