期刊
JOURNAL OF BIOLOGICAL CHEMISTRY
卷 295, 期 50, 页码 17298-17309出版社
ELSEVIER
DOI: 10.1074/jbc.RA120.015642
关键词
Escherichia coli; plasmid maintenance; chromosome dynamics; ATPase; DNA-protein interaction; repressor protein; Brownian ratchet; biolayer interferometry; ParB; partition complex; Escherichia coli (E; coli); plasmid; DNA-binding protein
资金
- Canadian Institutes of Health Research [133613]
The faithful segregation, or partition, of many low-copy number bacterial plasmids is driven by plasmid-encoded ATPases that are represented by the P1 plasmid ParA protein. ParA binds to the bacterial nucleoid via an ATP-dependent nonspecific DNA (nsDNA)-binding activity, which is essential for partition. ParA also has a site-specific DNA-binding activity to the par operator (parOP), which requires either ATP or ADP, and which is essential for it to act as a transcriptional repressor but is dispensable for partition. Here we examine how DNA binding by ParA contributes to the relative distribution of its plasmid partition and repressor activities, using a ParA with an alanine substitution at Arg(351), a residue previously predicted to participate in site-specific DNA binding. In vivo, the parA(R351A) allele is compromised for partition, but its repressor activity is dramatically improved so that it behaves as a super-repressor. In vitro, ParA(R351A) binds and hydrolyzes ATP, and undergoes a specific conformational change required for nsDNA binding, but its nsDNA-binding activity is significantly damaged. This defect in turn significantly reduces the assembly and stability of partition complexes formed by the interaction of ParA with ParB, the centromere-binding protein, and DNA. In contrast, the R351A change shows only a mild defect in site-specific DNA binding. We conclude that the partition defect is due to altered nsDNA binding kinetics and affinity for the bacterial chromosome. Furthermore, the super-repressor phenotype is explained by an increased pool of non-nucleoid bound ParA that is competent to bind parOP and repress transcription.
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