CPS operon

The capsule biosynthesis, or CPS operon is a section of the genome present in some Escherichia coli which regulates the production of polysaccharides which make up the bacterial capsule.[1] These polysaccharides help protect the bacteria from harsh environments, toxic chemicals, and bacteriophages.

The CPS operon contains genes which code for the following proteins:

• Wza - a lipoprotein which may form a channel in the bacterial outer membrane.[1]
• Wzb - a cytoplasmic regulatory phosphatase which dephosphorylates Wzc.[1]
• Wzc - a tyrosine kinase found in the bacterial inner membrane. Participates in polymerization of capsule polysaccharides.[1]
• Wzx - Transfers new polysaccharide units across the inner membrane.[1]
• Wzy - Assembles longer polysaccharide chains using units introduced by Wzx.[1]

The CPS operon is likely transcriptionally regulated by the Rcs (regulation of capsule synthesis) proteins.[1] Reduced levels of membrane-derived oligosaccharides result in autophosphorylation of RcsC. This results in a phosphate group being transferred from RcsC to RcsB. RcsB then binds to RcsA, forming a complex which acts on the CPS promoter and activates transcription of the CPS genes.

The same operon is present in Klebsiella species, possibly as a result of horizontal gene transfer.[1]