Glycosyltransferase that catalyzes the transfer of GlcNAc from UDP-GlcNAc to the GlcNAcbeta1-2Manalpha1-3 arm of the core structure of N-linked glycans through a beta1-4 linkage and participates in the production of tri- and tetra-antennary N-linked sugar chains (PubMed:10372966, PubMed:17006639). Prefers complex-type N-glycans over hybrid-types (PubMed:17006639). Has lower affinities for donors or acceptors than MGAT4A, suggesting that, under physiological conditions, it is not the main contributor in N-glycan biosynthesis (PubMed:17006639).
