Amino acids of the cholera toxin from differ from those of strain O 1 (

The isolates of Vibrio cholerae (Vc) non-O1 from the Sudanese outbreak in 1968 produce an enterotoxin similar to cholera toxin (CT) of Vc O1. However, we have observed that the subunit B of CT purified from a Sudanese isolate (strain $7) was a larger oligomer than that of Vc O1 (Yamamoto et al., 1983). This larger oligomer formation was suggested to be due to difference in the subunit B from CT of Vc O1 (Yamamoto et al., 1983). To clarify the possible aa change(s) in $7 CT, we cloned the structural genes (ctxAB) of $7 and determined the nt sequence of the gene. Vc non-O1 serovar 037 strain $7 (Yamamoto et al. 1983) was used for gene analysis. A ctxA probe-positive clone (pKY310) isolated from a gene library of whole bacterial DNA of $7 cloned in pUC18 was used for nt sequencing. The oligodeoxynucleotide primers for sequencing were selected from the reported nt sequence of ctxAB of Vc O1 strain 2125 (Mekalanos et al., 1983).