The gene encoding the heat-stable enterotoxin of Vibrio cholerae is flanked by 123-base pair direct repeats Ogawa, A.; Takeda, T. Microbiology and Immunology 37(8): 607-616 1993 0385-5600 10.1111/j.1348-0421.1993.tb01683.x https://eurekamag.com/research/009/580/009580565.php