The ability of bacteria to synthesise complex polysaccharide chains at a controlled number of repeating units has wide biological functions which include: symbiosis, biofilm formation and immune system avoidance. Complex polysaccharide chains such as the O antigen component of lipopolysaccharide and the enterobacterial common antigen (ECA) are synthesised by the most common polysaccharide synthesis pathway in bacteria, known as the Wzy-dependent pathway. The O antigen (B) and ECA (E) are polymerized into chains via the inner membrane proteins WzyB and WzyE, while the co-polymerases WzzB and WzzE, modulate the number of repeat units in the chains or “the modal length” of the polysaccharide via a hypothesised interaction. The data generated in this project is the first to show the phenomenon that WzzE is able to partially regulate O antigen modal length via a potential interaction with WzyB. To investigate this, one or both of the transmembrane regions (TM1 and TM2) of the co-polymerases (WzzE and WzzB) were swapped to create six chimera proteins. Several chimeric proteins were found to significantly increase O antigen modal length control, while others reduced modal length control, as detected via colicin E2 sensitivity assays, LPS analysis by SDS PAGE and silver-staining and ECA Western immunoblots. These results suggest that the TM2 region of Wzz proteins plays a critical role in O antigen and ECA modal length control presumably via the interaction with Wzy proteins.