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doi: 10.1242/10.1242/jcs.00187

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Sbh1p, a subunit of the Sec61 translocon, interacts with the chaperone calnexin in the yeast Yarrowia lipolytica

Laboratoire de Génétique moléculaire et cellulaire, INRA, CNRS, Institut National Agronomique Paris-Grignon, 78850 Thiverval-Grignon, France

^* Author for correspondence (e-mail: boisrame{at}grignon.inra.fr)

Accepted 24 September 2002

The core component of the translocation apparatus, Sec61p or , was previously cloned in Yarrowia lipolytica. Using anti-Sec61p antibodies, we showed that most of the translocation sites are devoted to co-translational translocation in this yeast, which is similar to the situation in mammalian cells but in contrast to the situation in Saccharomyces cerevisiae, where post-translational translocation is predominant. In order to characterize further the minimal translocation apparatus in Y. lipolytica, the ß Sec61 complex subunit, Sbh1p, was cloned by functional complementation of a sbh1, sbh2 S. cerevisiae mutant. The secretion of the reporter protein is not impaired in the Y. lipolytica sbh1 inactivated strain. We screened the Y. lipolytica two-hybrid library to look for partners of this translocon component. The ER-membrane chaperone protein, calnexin, was identified as an interacting protein. By a co-immunoprecipitation approach, we confirmed this association in Yarrowia and then showed that the S. cerevisiae Sbh2p protein was a functional homologue of YlSbh1p. The interaction of Sbh1p with calnexin was shown to occur between the lumenal domain of both proteins. These results suggest that the ß subunit of the Sec61 translocon may relay folding of nascent proteins to their translocation.

Key words: Translocation, Quality control, Sec61 ß