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

Abstract

Transposition of Ty elements in the yeast Saccharomyces cerevisiae occurs through an RNA intermediate. Although Ty RNA accounts for 5 to 10% of the total polyadenylated RNA in a haploid cell, the transposition frequency is only i0' to 10-8 per gene. To determine whether Ty elements native to the yeast genome are transpositionally competent, two elements were fused to the GALI promoter and tested for their ability to transpose. These native elements, Tyl-588 and Ty2-117, transposed at high levels when the GAL) promoter was induced. Three Ty's identified as spontaneous transpositions in specific target genes were also tested. Of these three, Ty2-917 and the previously characterized element Tyl-H3 were shown to be transpositionafly competent. The third element, Tyl-Hi, was transposition defective. In addition, we marked the chromosomal copy of Tyl-588 with the NEO gene and demonstrated that Tyl-588NEO was actively transcribed in yeast cells. Tyl-588NEO transcription was regulated by the SPT3 and MAT loci in the same manner as that observed for Ty's collectively. These results indicate that the yeast genome contains functional Ty elements. The presence of a transpositionally competent, actively transcribed element suggests that regulation of Ty transposition occurs at a posttranscriptional level.

T-body formation precedes virus-like particle maturation inS. cerevisiae

“…Although this is still an open question, we favor the idea that the kinetics of VLP formation is stimulated by locally concentrating Ty1 elements. In agreement with this, while the transposition level of endogenous Ty1 elements are very low, 26 ectopic expression of Ty1 stimulates T-body formation as well as VLP accumulation and transposition efficiency. 2,12,26 Alternatively, or in addition to this, VLP assembly into T-bodies may restrict the actions of host VLP destabilizing factors, such as Fus3p.…”

“…In agreement with this, while the transposition level of endogenous Ty1 elements are very low, 26 ectopic expression of Ty1 stimulates T-body formation as well as VLP accumulation and transposition efficiency. 2,12,26 Alternatively, or in addition to this, VLP assembly into T-bodies may restrict the actions of host VLP destabilizing factors, such as Fus3p. 27 In this scenario, the exit of mature VLPs from the T-bodies, or the dissolution of T-bodies altogether, may be required for the release of the preintegration complex (Int plus …”

Multiple LTR-Retrotransposon Families in the Asexual Yeast Candida albicans

“…Of the S. cerevisiae Ty elements, Ty1, Ty2, and Ty3 are known to be functional (Curcio et al 1988;Hansen and Sandmeyer 1990). Full-length, apparently uncorrupted, Ty4 elements are present, but they have not yet been shown to be active (Hug and Feldmann 1996).…”

Targeting Transposition: At Home in the Genome: Figure 1.

“…This is important and interesting because of a long-standing paradox in the Ty1 field (Curcio et al 1988). A significant percentage of cellular poly(A) + RNA is Ty1 RNA, yet transposition is normally infrequent.…”