Adds a GalNAc residue on to the Und-PP-Bac2,4diNAc-GalNAc disaccharide in the N-linked protein glycosylation pathway. Transfers the third sugar in the heptasaccharide biosynthesis. N-acetyl-alpha-D-galactosaminyl-(1->3)-N,N'-diacetyl-alpha-D-bacillosaminyl-tri-trans,hepta-cis-undecaprenyl diphosphate + UDP-N-acetyl-alpha-D-galactosamine = H(+) + 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 + UDP Protein modification; protein glycosylation. 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.