Role of Hsp70 Subfamily, Ssa, in Protein Folding in Yeast Cells, Seen in Luciferase-Transformed ssa Mutants

摘要

To investigate the role of constitutive hsp70 in protein folding and to probe the supplementation by other lisps in this folding, yeast cells expressing reduced constitutive hsp70 proteins, ssalssa2, were transformed with a plasinid expressing a bacterial luciferase protein. With several independent clone cells of transformants, the levels of luciferase activity and some lisps, such as hsplO4, hsp90, hsp70 and hsp26, were examined. The luciferase activity was significantly lower in ssalssa2 transformants than in the wild type (wt) cell transformed with the same plasmid. Among several clone cells of ssalssa2, the cells with higher luciferase activities exhibited higher amounts of Ssa4 which is known to be expressed instead of lacking Ssal and Ssa2. The luciferase activity closely correlated with the amount of Ssa proteins, more than with the amount of other lisps. It is suggested that constitutional Ssa "chaperones" are needed for the folding of proteins and, in cells lacking Ssal and Ssa2, the increased Ssa4 is thought to partly compensate for their role in the folding of luciferase in vivo.