Gene encoding the major subunit of CS1 pili of human enterotoxigenic Escherichia coli

Some enterotoxigenic strains of Escherichia coli (ETEC) utilize the CS1 pilus for colonization of human intestinal epithelium. We have cloned the gene which encodes the major CS1 subunit and called it cooA (for coli surface antigen one). Hybridization showed that the ETEC strain from which it was cloned carried cooA on a plasmid different from the one encoding its positive regulator, rns. Based on the cooA DNA sequence, cleavage with signal peptidase would be expected to produce a mature protein of 15.2 kDa; a 16-kDa polypeptide that reacted with CS1-specific antiserum was observed on electrophoresis. At the protein level, there was 92% similarity and 55% identity between cooA and cfaB, the major colonization factor antigen I (CFA/I) antigen. However, CS1-specific antisera did not react with CfaB. No hybridization was seen between either of two different cooA probes and total DNA from ETEC strains expressing AFA-1, CFA/I, CS2, CS3, CS4, CS5, or CS6.