Figure 1.

Toxicity of overexpressed N-end rule pathway is decreased by overexpressed Rpn1p and enhanced by overexpressed Rpt1p or Rpt6p. The S. cerevisiae strain JD52 (23) was transformed with pKM1313, a low-copy, URA3-based plasmid expressing UBR1 and RAD6 from the bidirectional P_GAL1,10 promoter (24). The pKM1313-containing JD52 cells were transformed either with the pRS425 vector (A), RPN1 (expressed from its own promoter in pRS425) (B), RPT1 (expressed from the P_CUP1 promoter in p314CUP1RPT1) (C), or RPT6 (expressed from the P_CUP1 promoter in p314CUP1RPT6) (D). (E and F) JD52 cells carrying both pKM1313 and the RPN1-expressing plasmid were further transformed with p314CUP1RPT1 (E) and p314CUP1RPT6 (F), respectively. Shown here are plates with cells grown in the galactose-containing minimal medium containing 0.2 mM CuSO₄ for 4 days at 30°C. On dextrose-containing plates (no overexpression of Ubr1p and Rad6p), all transformants grew at similar rates, irrespective of the presence of overexpressed Rpn1p, Rpt1p, or Rpt6p (data not shown).