Confers a modal distribution of chain length on the O-antigen component of lipopolysaccharide (LPS). Gives rise to a reduced number of short chain molecules and increases in numbers of longer molecules, with a modal value of 13 (in strain O111/M92) and of 17 (in strain K12). Bacterial outer membrane biogenesis; lipopolysaccharide biosynthesis. Belongs to the WzzB/Cld/Rol family.