The CAT-1 protein has two glycosylation sites, and both carry N-glycans [7] . Both sites are in the third extracellular loop which also contains the residues implicated in virus binding and entry [11, 12] . Both glycosylation sites were removed by PCR mediated site-specific mutagenesis from the dCAT-1 variant (Fig. 1) , and the resulting clone, dCAT-1-g, was transfected into MLV, nor did it result in syncytium formation by viruses not cytopathic in M. dunni cells. The transfectants, however, showed increased susceptibility to MoMLV compared to untransfected M. dunni cells (Table 3 , Exp.1), as also shown above for M. dunni(mCAT-1) ( Table 1) ; the transfectants showed no increase in their susceptibility to other ecotropic viruses. This is consistent with the conclusion that glycosylation of dCAT-1 is associated with MoMLV resistance.