Plus-strand strong-stop DNA transfer in yeast Ty retrotransposons.

The yeast Ty1 LTR retrotransposon replicates by reverse transcription and integration; the process shows many similarities to the retroviral life cycle. However, we show that plus strand strong-stop DNA transfer in yeast Ty1 elements differs from the analogous retroviral process. By analysis of the native structure of the Ty1 primer binding site and by a series of manipulations of this region and assessment of the effects on retrotransposition, we show that primer binding site inheritance is not from the tRNA primer, which is inconsistent with classical retroviral models. This unusual inheritance pattern holds even when the Ty1 primer binding site is lengthened in order to be more retrovirus-like. Finally, the distantly related Ty3 element has an inheritance pattern like Ty1, indicating evolutionary conservation of the alternative pathway used by Ty1. Based on these results we arrive at a plus strand primer recycling model that explains Ty1 plus strand strong-stop DNA transfer and inheritance patterns in the primer binding site.