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

The Ty element of yeast represents a class of eukaryotic transposons that show remarkable structural similarity to retroviral proviruses 1,2 . Recently, these comparisons have been strengthened by a series of observations on the yeast Ty element: (1) Ty transposes via an RNA intermediate 3 ; (2) it contains a sequence (Fig. 1) which, when translated, is homologous to a conserved region found in all reverse transcriptases 4,5 ; (3) a fusion protein encoded by Ty is produced by a frameshift event that is directly analogous to the production of Pr180 gag–pol in a retrovirus such as Rous sarcoma virus 5,6 . 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.