N-acetylglucosaminyltransferase that catalyzes the polymerization of single monomer units of UDP-N-acetylglucosamine to produce the linear homomer poly-beta-1,6-N-acetyl-D-glucosamine (PNAG, also referred to as PIA), a biofilm adhesin polysaccharide. Requires IcaD for full activity. Complete loss of the intercellular adhesion phenotype. Belongs to the glycosyltransferase 2 family.