Studies on the Role of dam Methylation at the Escherichia Coli Chromosome Replication Origin (oriC)

1984 ◽  
pp. 543-549 ◽  
Author(s):  
Patrick Forterre ◽  
Fatima-Zahra Squali ◽  
Patrick Hughes ◽  
Masamichi Kohiyama
Keyword(s):  
Escherichia Coli ◽  
Replication Origin ◽  
Chromosome Replication ◽  
Dam Methylation

scholarly journals The Consequences of Replicating in the Wrong Orientation: Bacterial Chromosome Duplication without an Active Replication Origin

mBio ◽  
2015 ◽  
Vol 6 (6) ◽  
Author(s):  
Juachi U. Dimude ◽  
Anna Stockum ◽  
Sarah L. Midgley-Smith ◽  
Amy L. Upton ◽  
Helen A. Foster ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Cell Viability ◽  
Replication Origin ◽  
Replication Fork ◽  
Chromosome Replication ◽  
Content Type ◽  
Rnase Hi ◽  
Independent Synthesis ◽  
Transcription And Replication ◽  
In Cells

ABSTRACTChromosome replication is regulated in all organisms at the assembly stage of the replication machinery at specific origins. InEscherichia coli, the DnaA initiator protein regulates the assembly of replication forks atoriC.This regulation can be undermined by defects in nucleic acid metabolism. In cells lacking RNase HI, replication initiates independently of DnaA andoriC, presumably at persisting R-loops. A similar mechanism was assumed for origin-independent synthesis in cells lacking RecG. However, recently we suggested that this synthesis initiates at intermediates resulting from replication fork fusions. Here we present data suggesting that in cells lacking RecG or RNase HI, origin-independent synthesis arises by different mechanisms, indicative of these two proteins having different rolesin vivo. Our data support the idea that RNase HI processes R-loops, while RecG is required to process replication fork fusion intermediates. However, regardless of how origin-independent synthesis is initiated, a fraction of forks will proceed in an orientation opposite to normal. We show that the resulting head-on encounters with transcription threaten cell viability, especially if taking place in highly transcribed areas. Thus, despite their different functions, RecG and RNase HI are both important factors for maintaining replication control and orientation. Their absence causes severe replication problems, highlighting the advantages of the normal chromosome arrangement, which exploits a single origin to control the number of forks and their orientation relative to transcription, and a defined termination area to contain fork fusions. Any changes to this arrangement endanger cell cycle control, chromosome dynamics, and, ultimately, cell viability.IMPORTANCECell division requires unwinding of millions of DNA base pairs to generate the template for RNA transcripts as well as chromosome replication. As both processes use the same template, frequent clashes are unavoidable. To minimize the impact of these clashes, transcription and replication in bacteria follow the same directionality, thereby avoiding head-on collisions. This codirectionality is maintained by a strict regulation of where replication is started. We have usedEscherichia colias a model to investigate cells in which the defined location of replication initiation is compromised. In cells lacking either RNase HI or RecG, replication initiates away from the defined replication origin, and we discuss the different mechanisms by which this synthesis arises. In addition, the resulting forks proceed in a direction opposite to normal, thereby inducing head-on collisions between transcription and replication, and we show that the resulting consequences are severe enough to threaten the viability of cells.

scholarly journals Analysis of Protein Synthesis Rates after Initiation of Chromosome Replication in Escherichia coli

1999 ◽  
Vol 181 (20) ◽  
pp. 6292-6299 ◽  
Author(s):  
Dorothée Bechtloff ◽  
Björn Grünenfelder ◽  
Thomas Åkerlund ◽  
Kurt Nordström
Keyword(s):  
Escherichia Coli ◽  
Protein Synthesis ◽  
Gel Electrophoresis ◽  
Polyacrylamide Gel Electrophoresis ◽  
Chromosome Replication ◽  
Peptide Mass ◽  
Initiation Of Replication ◽  
Mass Mapping ◽  
R1 Replicon

ABSTRACT The aim of this study was to investigate whether the synthesis rates of some proteins change after the initiation of replication inEscherichia coli. An intR1 strain, in which chromosome replication is under the control of an R1 replicon integrated into an inactivated oriC, was used to synchronize chromosome replication, and the rates of protein synthesis were analyzed by two-dimensional polyacrylamide gel electrophoresis of pulse-labeled proteins. Computerized image analysis was used to search for proteins whose expression levels changed at least threefold after initiation of a single round of chromosome replication, which revealed 7 out of about 1,000 detected proteins. The various synthesis rates of three of these proteins turned out to be caused by unbalanced growth and the synthesis of one protein was suppressed in theintR1 strain. The rates of synthesis of the remaining three could be correlated only to the synchronous initiation of replication. These three proteins were analyzed by peptide mass mapping and appeared to be the products of the dps, gapA, andpyrI genes. Thus, the expression of the vast majority of proteins is not influenced by the state of chromosome replication, and a possible role of the replication-associated expression changes of the three identified proteins in the cell cycle is not clear.

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