Reverse transcriptase activity and Ty RNA are associated with virus-like particles in yeast

Abstract

The Ty element of yeast represents a class of eukaryotic transposons that show remarkable structural similarity to retroviral proviruses. Recently, these comparisons have been strengthened by a series of observations on the yeast Ty element: Ty transposes via an RNA intermediate; it contains a sequence (Fig. 1) which, when translated, is homologous to a conserved region found in all reverse transcriptases; a fusion protein encoded by Ty is produced by a frameshift event that is directly analogous to the production of Pr180gag-pol in a retrovirus such as Rous sarcoma virus. Here we identify the reverse transcriptase activity that, until now, has been presumed to mediate Ty transposition and show that it is sequestered in virus-like particles that also contain Ty RNA.

The primer tRNA sequence is not inherited during Ty1 retrotransposition.

“…Otherwise, the putative mismatch might be corrected by DNA repair. Tyl-VLPs are cytoplasmically located (13,14); thus their DNA has presumably not been exposed to such correction. Tyl-VLPs were purified from strains VL30, -31, and -32.…”

“…Retrotransposon Tyl provides several advantages for studying reverse transcription; after induction of Tyl transcription, RNA-and DNA-containing VLPs accumulate in cells (13)(14)(15). VLP nucleic acid can be examined before integration.…”

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

“…1), we had obtained the first evidence for the existence of 1731 Gag-like proteins; indeed, 1731 Gag-fl-galactosidase fusion proteins were found into VLPs-containing, RTactive fractions extracted from Drosophila virilis transfected cells [12]. As Gag proteins from both retrotransposons and retroviruses have been repeatedly proven to be difficult to characterize when only the Mr was considered [24,25], we prepared antibodies directed against the central part of the 1731 Gag protein, assuming that they would allow recognition of gag products in cells and/or in organisms.…”

“…As orderly species of Gag proteins have been described in both retroviruses and retrotransposons [24,25], the appearance of a single immunoreactive 1731 Gag protein in the gradient fractions was surprising. In order to search other forms of 1731 Gag, we concentrated cytoplasmic particles by pelleting a postmitochondrial supernatant through a sucrose cushion, at 150,000 x g for one hour.…”

Escherichia coli RNase HI inhibits murine leukaemia virus reverse transcription in vitro and yeast retrotransposon Ty1 transposition in vivo

“…Ty1 VLPs were negatively stained with 2% uranyl acetate on thin carbon support films and micrographs were recorded at a magnification of 2 36 000 (Mellor et al 1985).…”