GDP-Man:Man1GlcNAc2-PP-Dol Alpha-1,3-Mannosyltransferase Activity

GDP-D-Mannose:D-Man-Beta-(1->4)-D-GlcNAc-Beta-(1->4)-D-GlcNAc-Diphosphodolichol 3-Alpha-Mannosyltransferase Activity

Catalysis of the reaction: beta-D-Man-(1->4)-beta-D-GlcNAc-(1->4)-D-GlcNAc-diphosphodolichol + GDP-alpha-D-mannose = alpha-D-Man-(1->3)-beta-D-Man-(1->4)-beta-D-GlcNAc-(1->4)-D-GlcNAc-diphosphodolichol + GDP + H+. This reaction is the transfer of an.