DISCONTINUITIES IN DNA SYNTHESIZED IN AN EXCISION-DEFECTIVE STRAIN OF ESCHERICHIA COLI FOLLOWING ULTRAVIOLET IRRADIATION
DISCONTINUITIES IN DNA SYNTHESIZED IN AN EXCISION-DEFECTIVE STRAIN OF ESCHERICHIA COLI FOLLOWING ULTRAVIOLET IRRADIATION
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DOI：
10.1016/0022-2836(68)90445-2
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发表时间：
1968-01-01
影响因子：
5.6
通讯作者：
HOWARDFL.P
中科院分区：
文献类型：
--
作者：
RUPP, WD;HOWARDFL.P
虽然E.大肠杆菌K12 uvrA 6在从其DNA切除嘧啶二聚体方面存在缺陷，37%的细胞在相当于约50个嘧啶二聚体/107个核苷酸的紫外线剂量下存活。掺入辐照细胞DNA中的氚化胸苷的量表明DNA中的嘧啶二聚体暂时抑制DNA合成。在碱性蔗糖梯度中进行单链DNA的区带沉降。为了使剪切降解最小化，将DNA从在梯度顶部分层的原生质球中释放。来自未辐照细胞的新合成的变性DNA沉积物的分子量大于100 × 106，而来自用60尔格/mm 2辐照的细胞的新合成的变性DNA的分子量约为14 × 106。在随后的辐照细胞的培养过程中，辐照后立即合成的DNA的沉降速率增加并接近正常DNA的沉降速率。在任何时候，在此孵育期间，掺入氚化胸苷快速沉降的DNA是最小的，这表明紫外线照射后合成的子链DNA含有间隙或碱不稳定的债券。这些双连续性在进一步培养过程中消失，因为发现沉降速率更高。这些子链缺陷的数量与亲本DNA中相同长度的嘧啶二聚体的数量相似。
Although E. coli K12 uvrA6 is defective in the excision of pyrimidine dimers from its DNA, 37% of cells survive a dose of UV light which is equivalent to about 50 pyrimidine dimers/107 nucleotides. The amount of tritiated thymidine incorporated into the DNA of irradiated cells indicates that pyrimidine dimers in the DNA temporarily inhibit DNA synthesis. Zone sedimentation of single-strand DNA was performed in alkaline sucrose gradients. To minimize degradation by shearing, the DNA was released from spheroplasts layered on top of the gradients. Newly synthesized denatured DNA from unirradiated cells sediments with a molecular weight of greater than 100 x 106, whereas the newly synthesized denatured DNA from cells irradiated with 60 ergs/mm2 has a molecular weight of about 14 x 106. During subsequent incubation of the irradiated cells, the sedimentation rate of the DNA synthesized immediately after irradiation increases and approaches that of normal DNA. At any time during this incubation period, the incorporation of tritiated thymidine into fast-sedimenting DNA is minimal suggesting that the daughter-strand DNA synthesized after UV-irradiation contains gaps or alkali-labile bonds. These dicontinuities disappear during further incubation, as a higher rate of sedimentation is found. The number of these daughter-strand defects is similar to the number of pyrimidine dimers in an equivalent length of parental DNA.