On-chip single-cell observation assay for propagation dynamics of yeast sup35 prionlike proteins

The cytoplasmically inherited genetic determinant [PSI⁺] of the yeast Sacchammyces cerevisiae is presumed to be a manifestation of the prionlike properties of the chromosome-encoded Sup35 protein. Here, we show the relationship between the cell growth and the inheritance of Sup35p-GFP aggregation using on-chip single-cell observation assay. When Sup35 was expressed by induction, an aggregation was started after soluble Sup35-GFP in the cytoplasm reached to the critical concentration. Once the aggregation was generated, the concentration of free Sup35-GFP remained constant at a critical value. After stopping the Sup35-GFP induction by changing the cultivation buffer, the concentration of soluble Sup35-GFP remained constant, whereas the size of aggregation decreased. This result indicates that the aggregation of Sup35-GFP is a reversible growth/shrinking phenomenon with the same velocity constant as that for a forward/reverse reaction.