Molecular cloning and nucleotide sequence of the colonization factor antigen I gene of Escherichia coli

The colonization factor antigen I (CFA/I) gene has been isolated and sequenced. The amino acid sequence of CFA/I deduced from the nucleotide sequence is composed of 170 amino acids. The first 23 amino acids are considered to be the signal peptide of the CFA/I protein since they are not present in the protein sequence. Among the remaining amino acids, only 2 are different from the protein sequence: amino acid position 76 is an aspartic acid instead of an asparagine, and position 97 is a serine instead of an alanine. The CFA/I gene has a typical Shine-Dalgarno sequence located 10 base pairs (bp) upstream from the initiation codon. The sequence TACAAT located 48 bp upstream from the initiation codon was tentatively designated the -10 sequence of the CFA/I gene promoter. No sequence homologous to the consensus -35 promoter sequence was found. A pair of inverted repeat sequences followed by a stretch of 8 A's are located 45 bp downstream from the termination codon of the CFA/I gene; this region may be a p-independent transcriptional terminator.