Pickett C L, Weinstein D L, Holmes R K
Department of Microbiology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814-4799.
J Bacteriol. 1987 Nov;169(11):5180-7. doi: 10.1128/jb.169.11.5180-5187.1987.
Operon fusions for the Escherichia coli heat-labile enterotoxin type IIa (LT-IIa) operon were isolated and characterized. The LT-IIa genes are organized in a transcriptional unit similar to those of cholera toxin (CT) and the closely related E. coli heat-labile toxin type I (LT-I, with subtypes LTh-I and LTp-I). The nucleotide sequence of the LT-IIa genes was determined and compared with the sequences of LTh-I and CT. The A subunit gene of LT-IIa was found to be 57% homologous with the A subunit gene of LTh-I and 55% homologous with the A gene of CT. Most of the homology derived from the region of the A gene which encodes the A1 fragment. The B gene of LT-IIa was not homologous with the B gene of LTh-I or CT. DNA probes containing various portions of the LT-IIa genes and adjacent sequences were used for hybridization studies with restriction endonuclease fragments of DNA from a collection of LT-II-producing strains. These studies showed that a probe containing much of the A subunit gene hybridized well to DNA from the various strains, but a probe for the B subunit gene did not.
分离并鉴定了大肠杆菌IIa型热不稳定肠毒素（LT-IIa）操纵子的操纵子融合体。LT-IIa基因组织成一个转录单元，类似于霍乱毒素（CT）以及密切相关的大肠杆菌I型热不稳定毒素（LT-I，有LTh-I和LTp-I亚型）的转录单元。测定了LT-IIa基因的核苷酸序列，并与LTh-I和CT的序列进行了比较。发现LT-IIa的A亚基基因与LTh-I的A亚基基因有57%的同源性，与CT的A基因有55%的同源性。大部分同源性来自于A基因中编码A1片段的区域。LT-IIa的B基因与LTh-I或CT的B基因不同源。含有LT-IIa基因不同部分和相邻序列的DNA探针用于与一组产LT-II菌株的DNA限制性内切酶片段进行杂交研究。这些研究表明，含有大部分A亚基基因的探针能与各种菌株的DNA很好地杂交，但B亚基基因的探针则不能。
