&9;Several processive glycosyl transferases have been implicated in transport. WbbF of Salmonella enterica sv. Borreze is one such enzyme. It consists of 459 amino acyl residues with 4 TMSs. It has a periplasmic domain immediately following a large cytoplasmic domain to which the glycosyl transferase activity resides. Cps35 of Streptococcus pneumoniae, HasA of Streptococcus pyogenes, IcaA of Staphylococcus epidermidis and several chitin synthases represent other examples of potential vectorial polymerases. The C-terminus of WbbF is thought to have pore-forming activity, but no direct evidence yet supports this postulate. If transport by these enzymes is demonstrated, it would provide evidence for "vectorial polymerization," a group translocation process. Over 500 homologues of WbbF are found in Gram-positive bacteria, Gram-negative bacteria, cyanobacteria, archaea and plants. These proteins vary in size from about 250 to about 750 amino acyl residues. However most of the functionally characterized bacterial glycosyl transferases are of 400-500 residues.