A subunit of the mammalian oligosaccharyltransferase, DAD1, interacts withMcl-1, one of the bcl-2 protein family

DAD1 is a mammalian, homologue of Saccharomyces cerevisiae Ost2p, a subunit of the oligosaccharyltransferase complex. Loss of its function induces apo ptosis in hamster BHK21 cells. By means of a two-hybrid method involving DA D1 as bait, the C-terminal region of Mcl-1, one of the bcl-2 family, was is olated. Consistently, DAD1 binds well to Mcl-1 in COS cells when overexpres sed, On deletion analysis, the C-terminal domain of Mcl-1 containing BH2 (b cl-2 homologous domain) was found to be essential for the interaction with DAD1, On the other hand, the C-terminal half of DAD1 was concluded to be es sential for the interaction with Mcl-1, Surprisingly, a Delta C-DAD1 mutant lacking only 4 amino acid residues from the C-terminus did not complement the tsBN7 mutation, while it interacted well with Mcl-1, In contrast, Delta N-DAD1 lacking 20 amino acid residues from the N-terminus still exhibited the ability to complement the tsBN7 mutation. Thus, the C-terminus of DAD1 was suggested to play an important role in N-linked glycosylation and to co mplement the tsBN7 mutation. Mcl-1 may be required for the inhibition, of a poptotic cell death caused by a loss of DAD1.