Raha M, Hutchinson F
Department of Molecular Biophysics and Biochemistry Yale University, New Haven, CT 06511.
J Mol Biol. 1991 Jul 20;220(2):193-8. doi: 10.1016/0022-2836(91)90001-m.
An Escherichia coli lysogen was constructed with a lambda phage bearing a lacZ gene surrounded by about 100 x 10(3) base-pairs of dispensable DNA. The lacZ mutants induced by gamma rays in this lysogen were more than 10% large deletions, ranging in size from 0.6 x 10(-3) to 70 x 10(3) base-pairs. These deletions were centered, not on lacZ, but on a ColE1 origin of DNA replication located 1.2 x 10(3) bases downstream from lacZ. This suggested that this origin of replication was involved in the process by which the deletions were formed. In agreement with this hypothesis, a lysogen of the same phage without the ColE1 origin showed a very much lower percentage of radiation-induced deletions, as did a second lysogen of a lambda phage without any known plasmid origin of replication. Indirect evidence is presented for radiation-induced deletions centered on the lambda origin of DNA replication in a lysogen. It is suggested that high percentages of large deletions may occur among radiation-induced mutations in mammalian cells because deletions centered on some of the thousands of origins of replication in these genomes do not kill the cells.
构建了一种大肠杆菌溶原菌，其携带的λ噬菌体带有一个lacZ基因，该基因被约100×10³个碱基对的可缺失DNA所包围。在此溶原菌中，由γ射线诱导产生的lacZ突变体有超过10%是大缺失，大小范围从0.6×10⁻³到70×10³个碱基对。这些缺失并非以lacZ为中心，而是以位于lacZ下游1.2×10³个碱基处的ColE1 DNA复制起点为中心。这表明该复制起点参与了缺失形成的过程。与这一假设相符的是，不含ColE1起点的同一噬菌体的溶原菌显示出辐射诱导缺失的比例非常低，没有任何已知质粒复制起点的λ噬菌体的另一种溶原菌也是如此。有间接证据表明，在一种溶原菌中，辐射诱导的缺失是以λ噬菌体的DNA复制起点为中心的。有人提出，在哺乳动物细胞的辐射诱导突变中可能会出现高比例的大缺失，因为以这些基因组中数千个复制起点中的一些为中心的缺失不会杀死细胞。
