Yamaguchi H, Yamashita T, Shimizu H, Ikeda H
Department of Molecular Biology, University of Tokyo, Japan.
Mol Gen Genet. 1995 Oct 25;248(6):637-43. doi: 10.1007/BF02191702.
To study the mechanism of spontaneous and UV-induced illegitimate recombination, we examined the formation of the lambda bio specialized transducing phage in Escherichia coli. Because most lambda bio transducing phages have double defects in the red and gam genes and have the capacity to form a plaque on an E. coli P2 lysogen (Spi- phenotype), we selected lambda bio transducing phage by their Spi- phenotype, rather than using the bio marker. We determined sequences of recombination junctions of lambda bio transducing phages isolated with or without UV irradiation and deduced sequences of parental recombination sites. The recombination sites were widely distributed on E. coli bio and lambda DNAs, except for a hotspot which accounts for 57% of UV-induced lambda bio transducing phages and 77% of spontaneously induced lambda bio transducing phages. The hotspot sites on E. coli and lambda DNAs shared a short homology of 9 bp. In addition, we detected direct repeat sequences of 8 bp within and near both the bio and lambda hotspots. A recA mutation did not affect the frequency of the recombination at the hotspot, indicating that this recombination is not a variant of recA-dependent homologous recombination. We discuss a model in which the short homology as well as the direct repeats play essential roles in illegitimate recombination at the hotspot.
为了研究自发和紫外线诱导的异常重组机制，我们检测了大肠杆菌中λbio特异性转导噬菌体的形成。由于大多数λbio转导噬菌体在red和gam基因上存在双重缺陷，并且能够在大肠杆菌P2溶原菌上形成噬菌斑（Spi-表型），我们通过其Spi-表型选择λbio转导噬菌体，而不是使用bio标记。我们测定了经紫外线照射或未经紫外线照射分离得到的λbio转导噬菌体的重组连接序列，并推导了亲本重组位点的序列。重组位点广泛分布于大肠杆菌bio和λDNA上，除了一个热点区域，该热点区域分别占紫外线诱导的λbio转导噬菌体的57%和自发诱导的λbio转导噬菌体的77%。大肠杆菌和λDNA上的热点位点共享9个碱基对的短同源性。此外，我们在bio和λ热点区域内及附近检测到8个碱基对的直接重复序列。recA突变不影响热点区域的重组频率，表明这种重组不是recA依赖性同源重组的变体。我们讨论了一个模型，其中短同源性以及直接重复序列在热点区域的异常重组中起重要作用。
