Function of DADl Protein in Programd Cell Death

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We have isolated a series of temperature sensitive growth mutant from the hamster BHK21 cell line. Among those ts mutants, we found the mutants which enter apoptotic cell death at the restrictive temperature. In one of them tsBN7, chromosomal DNA was fragmented with a typical manner like apoptptic cell death depending on protein synthesis. We have cloned a human gene complementing tsBN7 mutation and designated as DAD1 encoding a protein of 12.5 kDa which is well conserved through evolution. As a co-work, we have cloned a dadl homologue of Caenorhabditis elegans (Ce-dadl). Ce-dadl is more than 60% identical to vertebrate DAD1 in amino acid level and well complemented tsBN7 mutation. By overexpression, human DAD1 suppressed programd cell death in C.elegance.Recently, DAD1 was found to be a homologue of yeast OST2 involved in N linked glycosylation. Based on this finding, we found that a glycosylation of p450 is temperature sensitive in tsBN7 cells. As reported that N linked glycosylation occurs prior to entering Golgi apparatus, DAD1 seems to be located in endoplasmic reticulum. We don't know how a defect of N linked glycosylation causes apoptotic cell death. In order to clarify this issue, we are deleting DAD1 gene from mouse chromosome by gene targeting.