Coordinating Effect Of The Escherichia Coli DksA Protein In Replication Initiation,DNA Repair And Conflicts Between Replication And Transcription

Replication machine(replication forks)and RNA polymerases(RNAPs)collide with each other in a manner of either head-on or co-directional orientation.A transcribing RNAP blocks moving replisome,subsequently stalls the replisome,and eventually causes DNA double-strand breaks(DSBs).The Escherichia coli DksA and Mfd protein resolve the collision between replication fork and RNAP by dislodging RNAP from the template to restart replication with assistance of other factors.However,does the collision affect transcription?Here the paper showed that transcription level of gene in orientation of co-directional with replication was slighly increased relative to that in orientation of head-on in ABTGcasa medium.However,transcription level of gene in co-directional manner was slightly decreased in LB medium.In the abesence of DNA replication,transcription of the gene on leading strand was significantly higher than that of the gene on lagging strand;the increase was clear in the cells grown in LB while it was minor in ABTGcasa and the lowest in ABT.These results indicate that transcription frequency of the gene on leading strand is higher than that of the gene on lagging strand and the transcription frequency is in a nutrition-dependent manner.It has been shown that DksA is a nutrition-dependent transcription factor.Deletion of DksA released the gene transcriptions on lagging strand on plasmid yet not on chromosome in the cells grown in LB medium,the reason behind is unclear;deletion of DksA also released the gene transcriptions on leading strand either on plasmid or chromosome.Again,absence of DksA released transcription of the lagging strand gene on plasmid in the cells grown in ABTGcasa medium,however,the effect was not significat on leading strand.Deletion of Mfd significantly decreased transcription of the lagging strand gene and had no significant effect on transcription of the leading strand gene on plasmid in the cells grown in LB medium;however,absence of Mfd increased gene transcription in ABTGcasa medium.The result indicates that Mfd affects gene transcription on replication transcription collision and the effect is dependent on nutrition.These results indicate that DksA releases gene transcription arrested at replication-transcription collision,so does Mfd.The effects of both DksA and Mfd are dependent on nutrition.It was found that DksA affected initiation of replication and the effect was dependent on nutrition.?dksA mutant cells were sensitive to UV,nano-drug amine N-halamine polymeric nanoparticles(ANHP NPs)and zinc oxide(ZnO).And?dksA?recN double mutant were more sensitive to UV relative to single mutant.The results also suggest that DNA repair performed by RecN and DksA was independent of other DNA repair pathways.Hence,it is suggested that DksA and RecN only repair DNA lesion on replication-transcription collisions.