Pichia pastoris has discrete transitional ER sites and coherent Golgi stack
s, making this yeast an ideal system for studying the organization of the e
arly secretory pathway, To provide molecular tools for this endeavour, we i
solated P, pastel-is homologues of the SEC12, SEC13, SEC17, SEC18 and SAR1
genes. The P. pastoris SEC12, SEC13, SEC17 and SEC18 genes were shown to co
mplement the corresponding S. cerevisiae mutants, The SEC17 and SAR1 genes
contain introns at the same relative positions in both P. pastoris and S. c
erevisiae, whereas the SEC13 gene contains an intron in P. pastoris but not
in S, cerevisiae, Intron structure is similar in the two yeasts, although
the favoured 5' splice sequence appears to be GTAAGT in P. pastoris vs. GTA
TGT in S. cerevisiae. The predicted amino acid sequences of Sec13p, Sec17p,
Sec18p and Sar1p show strong conservation in the two yeasts. By contrast,
the predicted lumenal domain of Sec12p is much larger in P. pastoris, sugge
sting that this domain may help localize Sec12p to transitional ER sites. A
comparison of the SEC12 loci in various budding yeasts indicates that the
SEC12-related gene SED4 is probably unique to the Saccharomyces lineage. Ge
nBank Accession Nos are: SEC12, AF216960; SEC13, AF242186; SEC17, AF216957;
SEC18, AF216958; SAR1, AF216959; ACT1, AF216956. Copyright (C) 2000 John W
iley & Sons, Ltd.