Repeat unit polysaccharides of bacteria: a model for polymerization resembling that of ribosomes and fatty acid synthetase, with a novel mechanism for determining chain length

Mol Microbiol. 1993 Mar;7(5):725-34. doi: 10.1111/j.1365-2958.1993.tb01163.x.


We report the identification and sequence from Escherichia coli and Salmonella enterica strains of the cld gene, encoding the chain-length determinant (CLD) which confers a modal distribution of chain length on the O-antigen component of lipopolysaccharide (LPS). The distribution of chain lengths in the absence of this gene fits a model in which as the chain is extended there is a constant probability of 0.165 of transfer of growing chain to LPS core, with termination of chain extension. The data for E. coli O111 fit a model in which the CLD reduces this probability for short chains and increases it to 0.4 for longer chains, leading to a reduced number of short chain molecules but an increase in numbers of longer molecules and transfer of essentially all molecules by chain length 21. We put forward a model for O-antigen polymerase which resembles the ribosome and fatty acid synthetase in having two sites, with the growing chain being transferred from a D site onto the new unit at the R site to extend the chain and then back to the D site to repeat the process. It is proposed that the CLD protein and polymerase form a complex which has two states: 'E' facilitating extension and 'T' facilitating transfer to core. The complex is postulated to enter the E state as O-antigen polymerization starts, and to shift to the T state after a predetermined time, the CLD acting as a molecular clock. The CLD is not O-antigen or species-specific but the modal value does depend on the source of the cld gene.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Base Sequence
  • Carbohydrate Sequence
  • Escherichia coli / genetics
  • Escherichia coli / metabolism*
  • Escherichia coli Proteins*
  • Fatty Acid Synthases / metabolism*
  • Hexosyltransferases / metabolism
  • Lipopolysaccharides / metabolism*
  • Models, Biological*
  • Models, Molecular
  • Molecular Sequence Data
  • O Antigens
  • Polymers
  • Polysaccharides, Bacterial / genetics
  • Polysaccharides, Bacterial / metabolism*
  • Protein Conformation
  • Ribosomes / metabolism*
  • Salmonella typhimurium / genetics
  • Salmonella typhimurium / metabolism*
  • Sequence Alignment
  • Sequence Homology, Amino Acid


  • Bacterial Proteins
  • Escherichia coli Proteins
  • Lipopolysaccharides
  • O Antigens
  • Polymers
  • Polysaccharides, Bacterial
  • rol protein, Salmonella typhimurium
  • wzzB protein, E coli
  • rol protein, Bacteria
  • Fatty Acid Synthases
  • Hexosyltransferases
  • O-antigen polymerase, Salmonella

Associated data

  • GENBANK/Z17241
  • GENBANK/Z17278