PssP was demonstrated to be a PCP protein. It is a large inner membrane protein comprising a periplasmic domain with coiledcoils and two transmembrane segments. It was shown to be indispensable for EPS synthesis. The terminal stage in the assembly of EPS, i.e. the translocation of a polymer across the outer membrane, occurs through the pore formed by the PssN lipoprotein homologous to Wza protein. Bacterial two-hybrid assays provided evidence for interactions between proteins involved in EPS biosynthesis and transport, namely PssP-PssT and PssP-PssN, consistent with the notion of a multicomponent complex. Pss-I is likely not the only gene cluster involved in polysaccharide synthesis in R. leguminosarum RtTA1; several other regions with candidate genes were identified both in the chromosome and on a plasmid. One of them, the chromosomal Pss-II region, is comprised of several genes encoding putative homologues to constituents of the Wzx/ Wzy pathway,Aprotinin suggesting involvement in the synthesis of EPS or other polysaccharide. One of the proteins encoded within the Pss-II cluster is PssP2. Its primary and predicted secondary structure similarity, protein topology, and subcellular localization resembled PCP proteins and indicated a possibility of PssP2 engagement in the synthesis of LPS and/or EPS. To examine PssP2 involvement in the synthesis of either EPS or LPS, a mutant disrupted in the pssP2 gene was constructed. The significance of this qualitative change in the PssP2 protein for production of EPS and LPS and the symbiotic phenotype was studied. Moreover, the interrelations between PssP2 and thus far characterized Pss proteins were also examined. The results obtained indicate that the PssP2 protein is yet another component of the protein complex that plays an important role in EPS chainlength determination. Based on the results from the bacterial two-hybrid HJC0350 analysis, these proteins were proposed to interact with each other. In the case of the PssP protein, it was shown that deletions in different domains caused its inability to form homooligomeric structures, but did not completely diminish the protein’s property to interact with PssT. Mutants with shorter PssP variants produced EPS, in which LMW fractions dominated.