A complete isoleucyl-tRNA synthetase gene (ileS) of Campylobacter jejuni was isolated from a C. jejuni TGH9011 genomic DNA library constructed in pBluescript. The complete coding sequence, flanking regions and transcription start point were determined. The deduced isoleucyl-tRNA synthetase (IleRS) had 917 amino acids with a molecular mass of 105,399 Da, which was consistent with the observed size of 105 kDa in Escherichia coli maxicells. The ileS gene was mapped onto the physical map of the C. jejuni genome. Alignment of the C. jejuni IleRS sequence with six other bacterial IleRS sequences and two lower eukaryotic IleRS sequences identified seven conserved motifs, including the two signature sequences, HIGH and KMSKS, of class I aminoacyl-tRNA synthetases.