Billen D, Carreira L B, Hadden C T, Silverstein S J
J Bacteriol. 1971 Dec;108(3):1250-6. doi: 10.1128/jb.108.3.1250-1256.1971.
Freezing of Bacillus subtilis in liquid nitrogen results, upon thawing of the cells, in an enhanced deoxyribonucleoside triphosphate and reduced thymidine (Tdr) incorporation into cellular deoxyribonucleic acid (DNA). The DNA synthesized from thymidine triphosphate (TTP) was made by a "repair"-type system as determined by density transfer experiments. The mono- and diphosphate precursors were also incorporated by a "repair"-type synthesis. When Tdr was used as the radioactive precursor in the assay mixture, the product was only that expected from a semiconservative synthesis. Superlethal ultraviolet light exposure of the freeze-treated cells stimulated incorporation of phosphorylated precursors into DNA. Tdr uptake was greatly reduced by ultraviolet exposure, and only repair synthesis was observed. TTP and Tdr do not compete with one another in this system. The possibility that two DNA synthesizing systems exist in separate, non-mixing cellular compartments is considered.
将枯草芽孢杆菌在液氮中冷冻，细胞解冻后，脱氧核糖核苷三磷酸的掺入增强，而胸苷（Tdr）掺入细胞脱氧核糖核酸（DNA）的量减少。通过密度转移实验确定，由三磷酸胸苷（TTP）合成的DNA是由一种“修复”型系统合成的。单磷酸和二磷酸前体也通过“修复”型合成掺入。当在测定混合物中使用Tdr作为放射性前体时，产物仅是半保留合成所预期的。对冷冻处理的细胞进行超致死剂量的紫外线照射，刺激了磷酸化前体掺入DNA。紫外线照射使Tdr摄取大大减少，并且仅观察到修复合成。在该系统中，TTP和Tdr不相互竞争。考虑了在分开的、不混合的细胞区室中存在两种DNA合成系统的可能性。
