Consequently, the phenotypes observed in the pssP2:pKP2 and its complemented derivative may reflect disturbances in the interactions between the components of the chain-length determination system composed of at least three components: PssP, PssT, and PssP2. It was shown for Xanthomonas campestris and S. flexneri that the level of proteins engaged in polymerization of EPS UPF 1069 subunits or O-antigens, respectively, and their protein-protein interactions play an essential role in modulating the polymer chain length. The model in which PssP and PssP2 could serve opposite roles in determining the EPS length is further supported by their topologies. PssP was predicted to have four to five coiled coils. In the case of PssP2, only one periplasmic coiled-coil was predicted with high accuracy and one in the cytoplasmic domain, but with less confidence. The probability of coiled coil formation, location, and the number of the coiled-coil motifs is said to correlate with the degree of polymerization of the polysaccharides. If this were the case for PssP and PssP2, PssP would be responsible for HMW polymerization, while PssP2 for LMW polymerization. Moreover, the site of the mutation in PssP2 localizes near the secondary FK-3311 coiled-coil in the C-terminal domain of the protein. The C-terminal domain of PssP was not important for the interaction with PssT, but indispensable for homooligomerization. If that had been the case for PssP2, the short variant of the protein in the mutant might have disturbed either homooligomerization or interactions with other proteins. Contrary to an assembly model dependent on the stoichiometry of the complex members are the results showing that the chain length determining function of PCP proteins depends on certain amino acid residues. Previously, many mutagenesis studies on residues through Wzz proteins indicated that the function of modal chain length determination may be an overall property of the protein and may not be limited to one particular region. It was reported that the Wzz level did not correlate with the length of O-antigen chains in P. aeruginosa.