Effects of overexpression of Hsp70 and Hsp40 on HD exon 1 aggregation in yeast. (A) Total yeast lysates expressing HD exon 1 constructs and chaperones for 24 h were analyzed by filter-trap assays with and without prior incubation with SDS. Cells were either transformed with YEp105HD20Q and YEp105-HD53Q alone or with YEp105-HD53Q in combination with pGAL-SSA1, pGAL-SSB1, or pGAL-YDJ1 as indicated. Amounts of aggregation are given in arbitrary units normalized to the amounts of HD aggregation detected in cells expressing HD53Q alone. Note that the small amounts of aggregates of HD20Q are close to the background levels of the assay. (B) Cells expressing either myc-tagged HD20Q or HD53Q alone or HD53Q in combination with increased levels of Ssa1, Ssb1, or Ydj1 as in A were analyzed by immunofluorescence. (Left) Differential interference contrast photographs. (Right) HD fluorescence (red). DNA was stained with 4′,6-diamidino-2-phenylindole (blue). Examples representative of the majority of yeast cells examined are shown. Upon overexpression of Ssa1 or Ydj1 cells typically contained 3–5 distinct HD53Q deposits.