Cloning of murine glycosyl phosphatidylinositol anchor attachment protein,GPAA1

Glycosyl phosphatidylinositols (GPIs) are used to anchor many proteins to t he cell surface membrane and are utilized in all eukaryotic cells. GPI anch oring units are attached to proteins via a transamidase reaction mediated b y a GPI transamidase complex. We isolated one of the components of this com plex, mGPAA1 (murine GPI anchor attachment), by the signal sequence trap me thod. mGPAA1 cDNA is about 2 kb in length and encodes a putative 621 amino acid protein. The mGPAA1 gene has 12 small exons and 11 small introns. mGPA A1 mRNA is ubiquitously expressed in mammalian cells, and in situ hybridiza tion analysis revealed that it is abundant in the choroid plexus, skeletal muscle, osteoblasts of rib, and occipital bone in mouse embryos. Its expres sion levels and transamidation efficiency decreased with differentiation of embryonic stem cells. The 3T3 cell lines expressing antisense mGPAA1 faile d to express GPI-anchored proteins on the cell surface membrane.