Krishnan B R, Berg D E
Department of Molecular Microbiology, Washington University Medical School, St. Louis, Missouri 63110.
J Bacteriol. 1993 Feb;175(3):909-11. doi: 10.1128/jb.175.3.909-911.1993.
Dihydrofolate reductase (the folA gene product) catalyzes the synthesis of tetrahydrofolate, a key methyl donor in many biosynthetic pathways. Loss of folA had been thought to be lethal to wild-type (thyA+) Escherichia coli. Viable folA-null derivatives of thyA+ E. coli were obtained, however, by recombining a folA deletion linked to a Kanr selectable marker into a lambda folA+ phage and using this phage to transduce cells to kanamycin resistance. folA-null strains were slow growing, formed small colonies, and were auxotrophic for thymidine, adenine, methionine, glycine, and pantothenate.
二氢叶酸还原酶（folA基因产物）催化四氢叶酸的合成，四氢叶酸是许多生物合成途径中的关键甲基供体。folA的缺失曾被认为对野生型（thyA+）大肠杆菌是致死的。然而，通过将与卡那霉素抗性（Kanr）选择标记相连的folA缺失片段重组到λfolA+噬菌体中，并使用该噬菌体转导细胞获得卡那霉素抗性，从而得到了thyA+大肠杆菌的folA缺失但仍存活的衍生物。folA缺失菌株生长缓慢，形成小菌落，并且对胸苷、腺嘌呤、蛋氨酸、甘氨酸和泛酸盐营养缺陷。
