Attaches beta-O-GlcNAc (beta-O-N-acetyl-D-glucosamine) residues to the C3 position of poly(RboP)-wall teichoic acids (WTAs). Attenuates immunogenicity of WTA and protects S.aureus against adaptative host defenses by allowing bacteria to evade recognition by preexisting anti-S.aureus antibodies. Also protects the cell from podophage infection. 4-O-[(D-ribitylphospho)(n)-di{(2R)-glycerylphospho}]-N-acetyl-beta-D-mannosaminyl-(1->4)-N-acetyl-alpha-D-glucosaminyl di-trans,octa-cis-undecaprenyl diphosphate + n UDP-N-acetyl-alpha-D-glucosamine = 4-O-([3-N-acetyl-beta-D-glucosaminyl-1-D-ribitylphospho](n)-di{[2R]-1-glycerylphospho})-N-acetyl-beta-D-mannosaminyl-(1->4)-N-acetyl-alpha-D-glucosaminyl di-trans,octa-cis-undecaprenyl diphosphate + n H(+) + n UDP Cell wall biogenesis; poly(ribitol phosphate) teichoic acid biosynthesis. Homotrimer. Deletion of the gene leads to a substantially increased capacity of human neutrophils to phagocytose opsonized S.aureus. Inactivation renders the cell susceptible to podophages. TarP inhibitors could be used as a new strategy for rendering methicillin resistant Staphylococcus aureus (MRSA) strains susceptible to human host defenses. Belongs to the glycosyltransferase 2 family.