Isolation and nucleotide sequence determination of a gene encoding a heat-stable enterotoxin of Escherichia coli

An enterotoxin-producing strain of E. coli has been isolated from an infant patient in Shanghai Children Hospital and the gene of its heat-stable enterotoxin has been cloned and sequenced. The pre-pro-STI was composed of 72 amino acid residues corresponding to the encoding of 216 base pairs. There was only one nucleotide difference in the pro-part between this STI gene and the STIb gene reported in the literature. A guanosine base in our STI gene was substituted for a cytosine base in STIb gene resulting in a replacement of proline by alanine. Hence, the STI genes from different human sources are highly conserved though mutagenesis still occurs.