Processive glycosyltransferase that is part of the biosynthetic pathway of the lipid-linked oligosaccharide (LLO) that serves as the glycan donor in bacterial protein N-glycosylation. Catalyzes the transfer of exactly three alpha-(1->4)-N-acetylgalactosamine (GalNAc) units to the growing LLO precursor, GalNAc-alpha-(1->4)-GalNAc-alpha-(1->3)-diNAcBac-PP-undecaprenyl (PubMed:16186480, PubMed:19159314, PubMed:29386647). Cannot accept UDP-GlcNAc as substrate (PubMed:29386647). N-acetyl-alpha-D-galactosaminyl-(1->4)-N-acetyl-alpha-D-galactosaminyl-(1->3)-N,N'-diacetyl-alpha-D-bacillosaminyl-tri-trans,heptacis-undecaprenyl diphosphate + 3 UDP-N-acetyl-alpha-D-galactosamine = [alpha-D-GalNAc-(1->4)]4-alpha-D-GalNAc-(1->3)-alpha-D-diNAcBac-tri-trans,hepta-cis-undecaprenyl diphosphate + 3 H(+) + 3 UDP Protein modification; protein glycosylation. Contains an amphipathic helix (''ruler helix'') that has a dual role of facilitating membrane attachment and glycan counting. The ruler helix contains three positively charged side chains (Lys-67, Arg-71 and Lys-74) that can bind the pyrophosphate group of the LLO substrate and thus limit the addition of GalNAc units to three. N-linked protein glycosylation in C.jejuni consists in the transfer of a heptasaccharide (GalNAc-alpha1,4-GalNAc-alpha1,4-(Glcbeta1,3)-GalNAc-alpha1,4-GalNAc-alpha1,4-GalNAc-alpha1,3-bacillosamine) from a membrane-anchored undecaprenylpyrophosphate (Und-PP)-linked donor to the Asn side chain of proteins at the Asn-X-Ser/Thr motif. Belongs to the glycosyltransferase group 1 family.