Hdj1, the human homolog of Sis1, maintains strong but not weak [<i>PSI⁺</i>] variants in two yeast genetic backgrounds.

<p>(A) <i>sis1-Δ</i> cells from two backgrounds (W303 and 74D-694) bearing each of the six variants of [<i>PSI</i>⁺] examined in this study were transformed by a plasmid expressing Hdj1 from a constitutive promoter (<i>p424</i>-<i>GPD</i>-Hdj1) and subjected to plasmid shuffling to remove the covering Sis1-expression plasmid (<i>p316-SIS1-Sis1</i>). Color phenotype assays (<i>left</i>) are shown for representative transformants (<i>n</i>≥6 for each strain) following loss of the [<i>SIS1</i>-Sis1, <i>URA3</i>] plasmid. Maintenance or loss of each [<i>PSI</i>⁺] variant in these cells was also confirmed by semi-denaturing detergent agarose gel electrophoresis (SDDAGE) (<i>right</i>). Detergent resistant Sup35 aggregates indicative of the presence of [<i>PSI</i>⁺] were resolved by SDDAGE and visualized by immunoblot analysis using an antibody specific for Sup35. Control [<i>PSI</i>⁺] and [<i>psi</i>⁻] cells were included for comparison. (B) Lysates of all cells from (A) were resolved by SDS-PAGE and visualized by immunoblotting with Hdj1-specific antibodies that do not cross-react with Sis1. A lysate of a strain expressing only full-length Sis1 is included as a control. A band cross-reacting with the Hdj1 antibody in all lanes is shown as a loading control (<i>black arrow</i>).