Szalewska-Pałasz A, Wegrzyn A, Herman A, Wegrzyn G
Department of Molecular Biology, University of Gdańsk.
EMBO J. 1994 Dec 1;13(23):5779-85. doi: 10.1002/j.1460-2075.1994.tb06916.x.
Lambda plasmid DNA replication is inhibited in amino acid-starved wild type Escherichia coli strains (stringent response) but not in amino acid-starved relA mutants (relaxed response). This replication is perpetuated by the replication complex containing the lambda O protein (which is protected from proteases by other elements of the complex) and inherited by one of two daughter copies after a replication round. Since a fraction of stable lambda O protein was observed in relA- and relA+ strains, and negative regulation by the lambda Cro repressor does not seem to be important in the stringent or relaxed response of lambda plasmid replication to amino acid starvation, the inhibition of lambda plasmid replication in amino acid-starved wild type strains was investigated. lambda plasmids were unable to replicate in amino acid-starved relA- bacteria treated with rifampicin. Moreover, transcription from pR, which produces mRNA for replication protein synthesis and serves as transcriptional activation of ori lambda, was significantly decreased during the stringent response as well as in non-starved cells containing increased levels of ppGpp. However, it was little or totally not affected by the relaxed response. The replacement of pR with plac (which is known to be uninhibited by ppGpp) in a lambda plasmid resulted in its DNA replication during relaxed and stringent responses as well as during overproduction of ppGpp in unstarved bacteria. We conclude that ppGpp-mediated inhibition of transcriptional activation of ori lambda is responsible for inhibition of lambda plasmid DNA replication in amino acid-starved wild type strains.(ABSTRACT TRUNCATED AT 250 WORDS)
λ质粒DNA复制在氨基酸饥饿的野生型大肠杆菌菌株中受到抑制（严谨反应），但在氨基酸饥饿的relA突变体中不受抑制（松弛反应）。这种复制由包含λO蛋白的复制复合物维持（该蛋白受到复合物其他成分的保护，免受蛋白酶降解），并在一轮复制后由两个子代拷贝之一继承。由于在relA-和relA+菌株中均观察到一定比例的稳定λO蛋白，并且λCro阻遏物的负调控在λ质粒复制对氨基酸饥饿的严谨或松弛反应中似乎并不重要，因此对氨基酸饥饿的野生型菌株中λ质粒复制的抑制进行了研究。在用利福平处理的氨基酸饥饿的relA-细菌中，λ质粒无法复制。此外，在严谨反应期间以及在含有增加水平ppGpp的非饥饿细胞中，从pR转录产生用于复制蛋白合成的mRNA并作为ori λ转录激活的过程显著减少。然而，它几乎不受或完全不受松弛反应的影响。在λ质粒中用plac（已知不受ppGpp抑制）取代pR，导致其在松弛和严谨反应期间以及在未饥饿细菌中ppGpp过量产生期间进行DNA复制。我们得出结论，ppGpp介导的ori λ转录激活抑制是氨基酸饥饿的野生型菌株中λ质粒DNA复制受到抑制的原因。（摘要截短至250字）
