FIG. 9.

Models of type 3 polysaccharide synthesis and ejection. (A) Polysaccharide synthesis initiates on a lipid acceptor (open triangle) with membranes from WU2, JD614, or recombinant E. coli. Following ejection, the polysaccharide remains tethered to the membrane via the lipid acceptor. (B) Preformed polysaccharide (open symbols) of S. pneumoniae strain WU2 that is no longer associated with the membrane is extended (closed symbols) in the presence of both nucleotide sugars. Following ejection, the polysaccharide is released into the medium. Some of the preformed polysaccharide in WU2 may still contain its lipid anchor; thus, synthesis and ejection would resemble the scheme shown in panel A. Following ejection, all new polysaccharide synthesis occurs on the lipid acceptor as described in the legend to panel A, regardless of the initial acceptor.