Boye E, Krisch R E
Int J Radiat Biol Relat Stud Phys Chem Med. 1980 Feb;37(2):119-33. doi: 10.1080/09553008014550191.
Induction and repair of double- and single-strand DNA breaks have been measured after decays of 125I and 3H incorporated into the DNA and after external irradiation with 4 MeV electrons. For the decay experiments, cells of wild type Escherichia coli K-12 were superinfected with bacteriophage lambda DNA labelled with 5'-(125I)iodo-2'-deoxyuridine or with (methyl-3H)thymidine and frozen in liquid nitrogen. Aliquots were thawed at intervals and lysed at neutral pH, and the phage DNA was assayed for double- and single-strand breakage by neutral sucrose gradient centrifugation. The gradients used allowed measurements of both kinds of breaks in the same gradient. Decays of 125I induced 0.39 single-strand breaks per double-strand break. No repair of either break type could be detected. Each 3H disintegration caused 0.20 single-strand breaks and very few double-strand breaks. The single-strand breaks were rapidly rejoined after the cells were thawed. For irradiation with 4 MeV electrons, cells of wild type E. coli K-12 were superinfected with phage lambda and suspended in growth medium. Irradiation induced 42 single-strand breaks per double-strand break. The rates of break induction were 6.75 x 10(-14) (double-strand breaks) and 2.82 x 10(-12) (single-strand breaks) per rad and per dalton. The single-strand breaks were rapidly repaired upon incubation whereas the double-strand breaks seemed to remain unrepaired. It is concluded that double-strand breaks in superinfecting bacteriophage lambda DNA are repaired to a very small extent, if at all.
在将125I和3H掺入DNA后衰变以及用4 MeV电子进行外部照射后，对双链和单链DNA断裂的诱导和修复进行了测量。对于衰变实验，用5'-(125I)碘-2'-脱氧尿苷或(甲基-3H)胸苷标记的噬菌体λ DNA对野生型大肠杆菌K-12细胞进行超感染，并在液氮中冷冻。每隔一段时间取出等分试样，在中性pH下裂解，通过中性蔗糖梯度离心法检测噬菌体DNA的双链和单链断裂情况。所使用的梯度允许在同一梯度中测量两种类型的断裂。125I的衰变每产生一个双链断裂会诱导0.39个单链断裂。未检测到任何一种断裂类型的修复。每次3H衰变导致0.20个单链断裂和极少的双链断裂。细胞解冻后，单链断裂迅速重新连接。对于用4 MeV电子照射，用噬菌体λ对野生型大肠杆菌K-12细胞进行超感染，并悬浮在生长培养基中。照射每产生一个双链断裂会诱导42个单链断裂。断裂诱导率分别为每拉德和每道尔顿6.75×10(-14)（双链断裂）和2.82×10(-12)（单链断裂）。孵育时单链断裂迅速修复，而双链断裂似乎未得到修复。得出的结论是，超感染的噬菌体λ DNA中的双链断裂即使有修复，程度也非常小。
