CONSTITUTIVE EXPRESSION OF THE SOS RESPONSE IN RECA718 MUTANTS OF ESCHERICHIA-COLI REQUIRES AMPLIFICATION OF RECA718 PROTEIN
CONSTITUTIVE EXPRESSION OF THE SOS RESPONSE IN RECA718 MUTANTS OF ESCHERICHIA-COLI REQUIRES AMPLIFICATION OF RECA718 PROTEIN
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DOI：
10.1128/jb.169.2.728-734.1987
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发表时间：
1987-02-01
影响因子：
3.2
通讯作者：
ROEGNERMANISCALCO, V
中科院分区：
文献类型：
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作者：
MCCALL, JO;WITKIN, EM;ROEGNERMANISCALCO, V
在大肠杆菌的recA 718莱克萨+菌株中，SOS应答的诱导需要DNA损伤。这意味着RecA 718蛋白，像RecA+蛋白一样，必须通过由损伤引发的过程转化为活化形式（RecA*）以促进莱克萨（SOS基因的细胞阻遏物）的切割。然而，当莱克萨阻遏物活性被lexA缺陷型突变[莱克萨（Def）]消除时，携带recA 718基因（但不是recA+）的菌株显示出强烈的SOS突变体活性，并且能够在没有DNA损伤的情况下进行稳定的DNA复制（已知两种SOS功能需要RecA* 活性，即使不需要裂解莱克萨）。. recA 718莱克萨（Def）菌株的溶原细胞表现出原噬菌体的大量诱导，这表明其具有组成型切割噬菌体的能力。阻遏物当克隆的recA 718等位基因存在于质粒上的莱克萨+菌株中时，SOS突变体活性和β-在莱克萨控制下的半乳糖苷酶合成与质粒拷贝数成比例地表达。我们得出结论，RecA 718能够在没有DNA损伤的情况下被激活，以切割莱克萨和λ。阻遏物，但只有当它在莱克萨+菌株中扩增超过其基线水平时。在扩增水平，RecA 718也被组成型激活SOS诱变和稳定的DNA复制的作用。recA 718的核苷酸序列显示相对于recA+序列的两个碱基取代。我们建议，第一个允许蛋白质组成性激活，而第二个部分抑制这种能力。
In recA718 lexA+ strains of Escherichia coli, induction of the SOS response requires DNA damage. This implies that RecA718 protein, like RecA+ protein, must be converted, by a process initiated by the damage, to an activated form (RecA*) to promote cleavage of LexA, the cellular repressor of SOS genes. However, when LexA repressor activity was abolished by a lexA-defective mutation [lexA(Def)], strains carrying the recA718 gene (but not recA+) showed strong SOS mutator activity and were able to undergo stable DNA replication in the absence of DNA damage (two SOS functions known to require RecA* activity even when cleavage of LexA is not necessary). .lambda. lysogens of recA718 lexA(Def) strains exhibited mass induction of prophage, indicative of constitutive ability to cleave .lambda. repressor. When the cloned recA718 allele was present in a lexA+ strain on a plasmid, SOS mutator activity and .beta.-galactosidase synthesis under LexA control were expressed in proportion to the plasmid copy number. We conclude that RecA718 is capable of becoming activated without DNA damage for cleavage of LexA and .lambda. repressor, but only if it is amplified above its base-line level in lexA+ strains. At amplified levels, RecA718 was also constitutively activated for its roles in SOS mutagenesis and stable DNA replication. The nucleotide sequence of recA718 reveals two base substitutions relative to the recA+ sequence. We propose that the first allows the protein to become activated constitutively, whereas the second partially suppresses this capability.