The present invention provides methods to reduce or eliminate .alpha.-mannosidase resistant glycans on glycoproteins in yeast. The reduction or elimination of .alpha.-mannosidase resistant glycans on glycoproteins results from the disruption of the newly isolated P. pastoris AMR2 gene encoding .beta.1,2-mannosyltransferase. The present invention also discloses novel genes, polypeptides, antibodies, vectors and host cells relating to .alpha.-mannosidase resistance on glycans.