Protein disulphide isomerase genes of Kluyveromyces lactis

Two genes of Kluyveromyces lactis, KlPDI1 and KlMPD1, were studied. They code for a protein disulphide isomerase and its structural and functional homologue, respectively. The KlPDI1 product was 52.6% identical to Pdi1p and the KlMPD1 product 47% identical to Mpd1p of S. cerevisiae. Both genes contained the thioredoxin-active site-related signature. Their C-termini showed a new variant of the endoplasmic reticulum-retention signal, QDEL. A single copy of KlPDI1 was able to complement the growth defect of a pdi1 mutation. KlMPD1 on a multicopy vector partially suppressed the klpdi1 and pdi1 mutations. The Klpdi1 null mutation was lethal. The klmpd1 disruptant was viable, but showed an increased sensitivity to high temperature. Several stress response motifs were present in the upstream sequence of KlMPD1, but not of KlPDI1, whilst the opposite is known for the S. cerevisiae homologues. The viability of the klmpd1 mutant under starvation for nitrogen or carbon source was not different from that of the wild-type. The syntenic relationship is discussed for the KlPDI1 gene regions with respect to the duplicated segments PDI1/EUG1 in S. cerevisiae.