Schizosaccharomyces pombe ER oxidoreductin‐like proteins SpEro1a p and SpEro1b p

Endoplasmic reticulum oxidoreductins (Ero proteins) are essential for oxidation of protein disulphide isomerase (Pdi), which introduces disulphide bonds in target proteins. Contrary to the situation in Saccharomyces cerevisiae , with a single Ero protein (Ero1p), the genomes of Schizosaccharomyces pombe and of humans encode two Ero‐like proteins. Here we show that both Sz. pombe proteins (SpEro1a p and SpEro1b p) are N‐glycosylated and firmly associated with membranes of the secretory pathway. Surprisingly, only expression of SpEro1b p completely restores growth of the temperature‐sensitive S. cerevisiae ero1‐1 mutant, whereas SpEro1a p only partially complements this mutation. Upon expression in S. cerevisiae wild‐type cells, SpEro1b p leads to a significantly increased resistance to reductive stress by dithiothreitol, whereas SpEro1a p has only a marginal effect. These data suggest that SpEro1b p is a functional homologue of the S. cerevisiae Ero1p. Copyright © 2004 John Wiley & Sons, Ltd.