Lockman H, Kaper J B
J Biol Chem. 1983 Nov 25;258(22):13722-6.
We have determined the sequence of the DNA encoding the A2 (gamma) and B subunits of Vibrio cholerae enterotoxin. The order of the subunits as they would be transcribed is A2-B and the termination codon of the A2 subunit overlaps the initiation codon of the B subunit by four bases. Sequence analysis revealed a region capable of coding for a 21-amino acid leader peptide located at the NH2 terminus of the B subunit. While the nucleotide sequence homology between the cholera enterotoxin subunits and the analogous sequences of the genes for Escherichia coli heat-labile enterotoxin (LT) was 72 and 77% for the A2 and B subunits, respectively, the predicted amino acid sequences of the A2 subunits were less similar. Twenty-nine of 46 (63%) amino acids of the A2 subunits and 98 of 124 (79%) amino acids of the B subunits were identical between cholera enterotoxin and LT. The predicted amino acid sequence of the enterotoxin from a V. cholerae El Tor biotype strain reported here differs from the previously published amino acid sequences of the toxin from a classical biotype of V. cholerae at seven residues. Comparison of the A2 and B amino acid sequences among El Tor and classical biotypes of V. cholerae and E. coli LT demonstrates two regions of highly conserved sequences: 12 and 22 uninterrupted amino acids are the same among the A2 and B subunits, respectively, from the three strains.
我们已经确定了编码霍乱弧菌肠毒素A2（γ）和B亚基的DNA序列。这些亚基转录时的顺序是A2 - B，且A2亚基的终止密码子与B亚基的起始密码子重叠四个碱基。序列分析显示，在B亚基的NH2末端有一个能够编码21个氨基酸前导肽的区域。虽然霍乱肠毒素亚基与大肠杆菌不耐热肠毒素（LT）基因的类似序列之间的核苷酸序列同源性，A2亚基和B亚基分别为72%和77%，但A2亚基预测的氨基酸序列相似性较低。霍乱肠毒素和LT的A2亚基46个氨基酸中有29个（63%）相同，B亚基124个氨基酸中有98个（79%）相同。此处报道的霍乱弧菌埃尔托生物型菌株肠毒素的预测氨基酸序列与先前发表的霍乱弧菌古典生物型毒素的氨基酸序列在7个残基处不同。对霍乱弧菌埃尔托生物型和古典生物型以及大肠杆菌LT的A2和B氨基酸序列进行比较，发现有两个高度保守序列区域：来自这三个菌株的A2和B亚基分别有12个和22个连续相同的氨基酸。
