Among the variety of membrane-linked or extracellular polysaccharides excreted by bacteria, only capsular polysaccharides, lipopolysaccharides and teichoic acids have been shown to be exported by ABC transporters. A typical system is made of a conserved IM and an ABC ( Pubmed : 8858578 ) . In addition to these proteins, capsular polysaccharide exporter systems require two "accessory" proteins to perform their function: a periplasmic (E. coli) or a lipid-anchored outer membrane protein called OMA (Neisseria meningitidis and Haemophilus influenzae for example) and a cytoplasmic membrane protein MPA2 ( Pubmed : 9274022 ) . The proteins that are common to the CLS family (IM and ABC) segregate within two distinct clusters corresponding to capsular polysaccharide exporters and lipopolysaccharide exporters respectively. The IM and ABC of extracellular polysaccharide (such as teichoic acids) exporters in several Gram-positive bacteria, mycobacteria and archaebacteria cluster in the lipopolysaccharide-specific group of sequences.