Figure 1: Genetic organisation of cnl and cps loci in N. meningitidis.

Schematic organisation of the capsule synthesis (cps) island in meningococci. Serogroups A, B/C, W/Y and E are represented. Region A (light blue) is accompanied by Region C (bright green) encoding four capsule transport encoding genes ctrA-D. Region E (navy) encodes tex, a gene of unknown function homologue of a transcription factor. Region A-C-E is flanked by an inverted repeat segment, Region D and Region D’. Region D contains galE1 (black), encoding the UDP-galactose 4-epimerase and three genes termed rfbBAC (red) of unknown function. Region D’ contains a truncated galE2 (grey) and rfbB2-A2-C2 (red). Region B (yellow) contains ctrE and ctrF which encode KDO transferases to initiate polysaccharide biosynthesis. Region A (light blue) contains polysaccharide biosynthesis genes specific for each serogroup and ctrG (brown) which is found in cps islands encoding sialic acid biosynthesis pathways. The four genes csaA, csaB, csaC and csaD are required for the synthesis of a homopolymer of O-acetylated, α1 → 6-linked ManNAc 1-phosphate of serogroup A meningococci. Serogroup B, C, W and Y meningococci contain three genes required for sialic acid biosynthesis, cssA, cssB and cssC. Each cluster has a serogroup specific polysialyltransferase, capsule synthesis serogroup B (csb), capsule synthesis serogroup C (csc), capsule synthesis serogroup W (csw) and capsule synthesis serogroup Y (csy). Serogroup C polysaccharides are O-acetylated by CssE while serogroup Y/W are acetylated by CssF. The biosynthesis cluster for serogroup W and Y also contains a galU encoding a UTP:α-D-glucose-1-phosphate uridylyltransferase. Serogroup B consists of a homolpolymer of α2 → 8 linked sialic acid, serogroup C consists of α2 → 9 linked sialic acid, serogroup W consists of repeating units of 4-O-α-D-galactopyranosyl-β-D-N-acetylneuraminic acid and serogroup Y consists of repeating units of 4-O-α-D-glucopyranosyl-β-D-N-acetylneuraminic acid. Serogroup E polysaccharide consists of alternating D-galactosamine and 2-keto-3-deoxyoctulosonate (KDO) residues synthesized by the seven genes cseA-G. The capsule null locus (cnl) of non-disease causing meningococci consists of galE-rfbBAC and tex. The figure was drawn using Easyfig⁵⁰ and is similar to the figure presented by Harrison et al.⁴⁶.