Functional organization of the retrotransposon Ty from Saccharomyces cerevisiae: Ty protease is required for transposition.

Abstract

We used several diutations generated in vitro to further characterize the functions of the products encoded by the TyB gene of the transpositionally active retrotransposon TyH3 from Saccharomyces cerevisiae. Mutations close to a core protein domain of TyB, which is homologous to retroviral proteases, have striking effects on Ty protein processing, the physiology of Ty viruslike particles, and transposition. The Ty protease is required for processing of both TyA and TyB proteins. Mutations in the protease resulted in the synthesis of morphologically and functidnafly aberrant Ty viruslike particles. The mutant particles displayed reverse transcriptase activity, but did not synthesize Ty DNA in vitro. Ty RNA was present in the mutant particles, but at very low levels. Transposition of a genetically tagged element ceased when the protease domain was mutated, demdnstrating that Ty protease is essential for transposition. One of these mutations also defined a segment of TyB encoding an active reverse trnstriptase. These results indicate that the Ty protease, like its retroviral cohnterpart, plays an important role in particle assembly, replication, and transposition of these elements.

Transpositional competence and transcription of endogenous Ty elements in Saccharomyces cerevisiae: implications for regulation of transposition.

“…To investigate these possibilities, the transpositional competence of the GAL]-promoted elements in an spt3-101 mutant background was determined. In spt3-10 mutants, only aberrant Ty transcripts are produced from endogenous elements, which probably accounts for the absence of transposition of chromosomal elements (4,48). However, transposition induction of pGTyl-H3NEO in spt3-101 mutants results in high levels of transposition of the NEO-marked element (4).…”

“…6). Tyl-588 mapped to the same position in both strains BWG1-7A and GRF167 (Table 5 (48). However, the inhibitor may work at the level of Ty protein processing or viruslike particle formation.…”

“…It appears that the tyb-2098 mutation is carried in several Ty elements native to the yeast genome (1). Other mutations made in the consensus protease region of TyB abolish transposition of the GALl-promoted element (48).…”

“…Several mutant elements have been described that do not induce high levels of transposition when expressed from the GALI promoter (1,48 missense mutation, designated tyb-2098, in the consensus integrase region of Tyl-173, an element isolated as an insertional mutation in the LYS2 gene (38). It appears that the tyb-2098 mutation is carried in several Ty elements native to the yeast genome (1).…”

The Gag polypeptides of the Drosophila 1731 retrotransposon are associated to virus‐like particles and to nuclei

“…However, pol-derived enzymes are not the only proteins involved in transposition: structural Gag proteins were reported to play an active r61e in the replication/ transposition cycle of retroelements. In the yeast-Saccharomyces cerevisiae, the importance of both Gag and Gag-Pol polyproteins on transposon replication/transposition was established through the demonstration that synthesis of Gag protein is a necessary and essential step to support the Tyl transposition events [9][10][11]. Besides, the complex mechanism of the Gag processing could be one of the targets for a control strategy.…”