Sequence analysis of the colonization factor antigen 1 gene of ETEC and observation of CFA/1 recombinant clone with...

The structure gene of the colonization factor antigen 1 (CFA/1) has been sequenced. The amino acid sequence of CFA/1 precursor 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/1 protein. On the basis of the nucleotide sequence, three amino acids are different from the protein sequence. Amino acid residues at positions 37, 76 and 97 are found to be Ala, Asp and Ser, instead of Val, Asn and Ala as determined by amino acid sequencing. The CFA/1 is very hydrophobic amino acids. Among the total 170 amino acids, 47% of them are hydrophobic amino acids. CFA/1 gene has a typical Shine-Dalgarno sequence and-10 sequence, but no 35 promoter sequence could be found. The G + C ratio of CFA/1 gene is 40%. Observation of negatively stained preparations of the culture with electron microscopy showed that no fimbriae were found on E. coli C600 strain itself, but the cell carrying the plasmid showed thick pili on its surface.