Models we propose to explain <i>de novo</i> Sup35 aggregation.

<p><b>A.</b> The stages of the induced appearance of [<i>PSI⁺</i>] <i>de novo</i>. Induction of [<i>PSI⁺</i>] by overexpression of fluorescently-labeled Sup35 in [<i>PIN⁺</i>][<i>psi^-</i>] cells displays early Sup35 fluorescent foci ranging from one to a few dots, one of which is located near the vacuole (shown as darker green). At this perivacuolar Hsp42 protein deposit site, preexisting heterologous aggregates such as [<i>PIN⁺</i>] or Pin4C cross-seed the <i>de novo</i> aggregation of Sup35 (see panel B). Later, short lines appear to emanate from this dot towards the periphery of the cell while dots away from the vacuole disappear. Peripheral rings appear next, followed by perivacuolar internal rings. <b>B.</b> The cross-seeding model to explain how heterologous aggregates facilitate <i>de novo</i> Sup35 aggregation. Preexisting [<i>PIN⁺</i>]/Pin4C aggregates (shown in red ‘L’ shape) located at the Hsp42 protein deposit near the vacuole physically interact with soluble misfolded Sup35 proteins (shown as purple marbles). This interaction causes Sup35 to form oligomers. Then, Sup35 grows in length in a homotypic manner. Based on our data, we propose that [<i>PIN⁺</i>]/Pin4C aggregates can also grow in length laterally guided by Sup35 fibrils. Over time, laterally growing [<i>PIN⁺</i>]/Pin4C aggregates are less frequent. For simplicity, only two fibrils are depicted.