The Regulatory Mechanisms Of The Torr Protein On Gene Expression And Initiation Of Dna Replication In Escherichia Coli

In order to reveal the role of TorS/TorR in cell cycle regulation,we measured the cell cycle parameters of AtorS and AtorR mutants by flow cytometry.We found that the average number of origins for replication(oriCs)per cell and doubling time in AtorS cells were the same as that in the wild type cells while the average number of oriCs in AtorR cellswas more than that in wild type cells.The results indicate that absence of the TorR leads to an early initiation of replication.Strangely,neither overexpression of TorR nor co-expression of TorR and TorS could reverse the phenotype of AtorR mutant.However,extra SufD both in the wild type and?torRcells resulted in early initiation of replication,and the AsufDand?torR?sufDcells lead a late initiation of replication.In addition,the expression of sufD is higher in AtorR cells compared with the wide type cells.Thus,we conclude that TorR might regulate the DNA replication initiation through affecting the expression of the sufD gene.Cell cycle-dependent temporal transcription of genes is achieved by different mechanisms including a dynamic interaction of activator and repressor proteins with promoters,accumulation and/or degradation of key regulators,phosphorylation or dephosphorylation of regulatorsas a function of cell cycle.We find that the response regulator TorR protein of the TorR/TorS two component signal transduction targets the old pole of the Escherichia coli cell as a focus.Importantly,co-localization of TorR focus with chromosomal DNA is dependent on cell cycle progression and by which regulates transcription of a number of genes associated with Fe2+ transport,enterobactin synthesis and transport,Fe-S cluster assembly.Formation and polar localization of the TorR focus requires the presence of and the interaction with MreB,and DnaK proteins and ATP,suggesting that TorR delivering requires cytoskeleton organization and ATP provided energy.Either the signal receiver or the response regulator domain of TorR protein is also needed for the formation,polar localization of TorR focus and its interaction with MreB or DnaK.Absence of the protein-protein interactions and ATP lead to a loss in function of TorR as a transcription factor.Also FtsZ-ring formation seems to be a signal for formation of TorR focus,ensuring each daughter cell receives a TorR focus.We present a different mechanism for timing of cell cycle-dependent gene transcription where a transcription factor interacts with its target genes at a specific time point of cell cycle by controlling its spatial distribution.