Figure 2.
PRT1 directs degradation of an F-β-gal test protein in yeast. Pulse chase experiments followed by immunoprecipitation of F-β-gal protein, electrophoretic separation, and detection by fluorography indicated that a decreased F-β-gal steady-state level is caused by metabolic instability. Lanes 1 to 3, Wild-type (UBR1) yeast cells were used to indicate metabolic instability of F-β-gal. Lanes 4 to 6, Expression of PRT1 in yeast cells with disrupted UBR1 results in instability of F-β-gal. Lanes 7 to 9, Yeast cells without UBR1 (and without PRT1) cannot degrade F-β-gal. Left, Positions of Mr marker bands. Dot, Position of mature F-β-gal on the gel. Asterisk, Metabolically stable β-gal fragment that is formed in yeast as a side product.