Gudas L J, Mount D W
Proc Natl Acad Sci U S A. 1977 Dec;74(12):5280-4. doi: 10.1073/pnas.74.12.5280.
Treatments that inhibit DNA synthesis in recA(+)lexA(+)Escherichia coli stimulate synthesis of a 40,000 molecular weight protein species (protein X). The protein X molecules produced by wild-type and mutant E. coli strains have been compared by two-dimensional gel electrophoresis. One recA mutant (DM1415 spr recA1) produced a protein X with a more acidic isoelectric point than protein X from the wild type, demonstrating that protein X is probably the product of the recA gene. Additional mutants carrying the recA-linked tif-1 mutation yielded a protein X that was more basic than the wild-type protein, indicating that the tif-1 mutation also alters the recA protein. Protein X molecules from the above mutants and wild-type E. coli have been shown to yield similar partial products upon limited proteolysis in sodium dodecyl sulfate, indicating they are the same protein species. These and additional studies suggest that (i) the tif-1 mutation alters a site on the recA protein that is sensitive to DNA synthesis inhibition, (ii) synthesis of recA protein is self-regulated, and (iii) synthesis of recA protein is also regulated by the lexA product with lexA-suppressor mutations such as spr resulting in constitutive synthesis of recA protein.
在recA(+)lexA(+)大肠杆菌中抑制DNA合成的处理会刺激一种分子量为40,000的蛋白质（蛋白质X）的合成。通过二维凝胶电泳比较了野生型和突变型大肠杆菌菌株产生的蛋白质X分子。一种recA突变体（DM1415 spr recA1）产生的蛋白质X的等电点比野生型的蛋白质X更酸，这表明蛋白质X可能是recA基因的产物。携带与recA连锁的tif-1突变的其他突变体产生的蛋白质X比野生型蛋白质更碱性，表明tif-1突变也改变了recA蛋白。已证明上述突变体和野生型大肠杆菌的蛋白质X分子在十二烷基硫酸钠中进行有限蛋白酶解时会产生相似的部分产物，表明它们是同一蛋白质种类。这些及其他研究表明：（i）tif-1突变改变了recA蛋白上对DNA合成抑制敏感的位点；（ii）recA蛋白的合成是自我调节的；（iii）recA蛋白的合成也受lexA产物调节，lexA抑制子突变如spr会导致recA蛋白的组成型合成。
