title: Codon pairs in the genome of Escherichia coli.
abstract: BACKGROUND
  The effect of two neighboring codons (codon pairs) on gene expression is mediated via the interaction of their cognate tRNAs occupying the two functional ribosomal sites during the translation elongation step. For steric reasons it is reasonable to assume that not all combinations of codons and therefore of tRNAs are equally favorable when situated on the ribosome surface. Aiming of identifying preferential and rare codon pairs, we have determined the frequency of occurrence of all possible combinations of codon pairs in the entire genome of Escherichia coli (E.coli).
  
  
  RESULTS
  The frequency of occurrence of the 3904 codon pairs comprising both sense:sense and sense:stop codon pairs in the full set of E.coli 4289 ORFs was found to vary from zero to 4913 times. For most of the pairs we have observed a significant difference between the real and statistically predicted frequency of occurrence. The analysis of 334 highly expressed and 303 poorly expressed E.coli genes showed that codon pair usage is different for the two gene categories. Using an especially defined criterion (Delta(REG)), the codon pairs are classified as 'hypothetically attenuating' (HAP) and 'hypothetically non-attenuating' (HNAP) and their possible effect on translation is discussed.
  
  
  BACKGROUND
  The program used in this study is available at http://www.bio21.bas.bg/codonpairs/
authors.affiliation: Department of Gene Regulations, Institute of Molecular Biology, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria. svetlana@obzor.bio21.bas.bg
authors.forename: Svetlana
authors.initials: S
authors.lastname: Boycheva
authors.forename: Georgi
authors.initials: G
authors.lastname: Chkodrov
authors.forename: Ivan
authors.initials: I
authors.lastname: Ivanov
mesh_terms: D000465:Algorithms; D003062:Codon / Q000145:classification* / Q000235:genetics*; D030561:Databases, Nucleic Acid; D004926:Escherichia coli / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics; D005787:Gene Frequency / Q000235:genetics; D016680:Genome, Bacterial; D014176:Protein Biosynthesis / Q000235:genetics*; D017422:Sequence Analysis, DNA / Q000379:methods*
chemical_list: D003062:Codon