chi*, a chi-related 11-mer sequence partially active in an E-coli recC* strain
chi*, a chi-related 11-mer sequence partially active in an E-coli recC* strain
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DOI：
10.1046/j.1365-2443.1997.1410339.x
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发表时间：
1997-08-01
期刊：
影响因子：
2.1
通讯作者：
Kobayashi, I
中科院分区：
文献类型：
--
作者：
Handa, N;Ohashi, S;Kobayashi, I
背景：大肠杆菌的CHI序列(5‘GCTGGTGG)最早被鉴定为增加噬菌体lambda噬菌斑大小的位点。随后的研究表明，该位点对RecBCD外切酶活性的减弱和RecA、RecBCD介导的重组的促进都有作用。已知含有chi位点的噬菌体lambda在recc(*)(RecC1004)突变体上会产生非常小的空斑，因为chi不被recbc(*)D突变体酶识别。这些片段被发现共享一个类似CHI的11聚体序列，5‘GCTGGTGCTCG。用该序列的合成11-聚体替换这些片段以及对其最后四个核苷酸的单碱基替换分析表明，该序列对于观察到的活性既是必要的，也是充分的。该序列被命名为chi(*)(chi-star)，保护了recc(*)突变体和RecBCD(+)菌株中的滚环DNA复制，很可能是因为它减弱了RecBC(*)D和RecBCD(+)酶的外切酶活性。在两次实验中，没有显著刺激lambda重组。结论：我们发现在体内，突变的RecBCD酶对较长的chi变体有反应。
Background: chi sequence (5'GCTGGTGG) of Escherichia coli was first identified as a site that increased the plaque size of bacteriophage lambda. Subsequent studies showed that this site is responsible for both the attenuation of RecBCD exonuclease activity and the promotion of RecA, RecBCD-mediated recombination. It is known that bacteriophage lambda containing the chi site makes very small plaques on a recC(*) (recC1004) mutant because chi is not recognized by the RecBC(*)D mutant enzyme.Results: We cloned E. coli chromosomal fragments in chi which allowed chi to form larger plaques on this recC(*) mutant. The fragments were found to share a chi-like 11-mer sequence, 5'GCTGGTGCTCG. Substitution of these fragments with a synthetic 11-mer of this sequence and single-base-pair substitution analysis of its last four nucleotides demonstrated that this sequence is both necessary and sufficient for the observed activity. The sequence, designated chi(*) (chi-star), protected rolling-circle DNA replication in the recC(*) mutant and in the recBCD(+) strain, most likely because it attenuated the exonuclease activity of the RecBC(*)D and RecBCD(+) enzyme. chi(*), did not significantly stimulate lambda recombination in two assays.Conclusion: We have discovered that a mutant RecBCD enzyme responds, in vivo, to a longer chi variant.