Transcriptional control for initiation of chromosomal replication in Escherichia coli: fluctuation of the level of origin transcription ensures timely initiation.
BACKGROUND
During the cell cycle, the initiation of chromosomal replication is strictly controlled. In Escherichia coli, the initiator DnaA and the replication origin oriC are major targets for this regulation. Here, we assessed the role of transcription of the mioC gene, which reads through the adjacent oriC region. This mioC-oriC transcription is regulated in coordination with the replication cycle so that it is activated after initiation and repressed before initiation.


RESULTS
We isolated a strain bearing a mioC promoter mutation that causes constitutive mioC-oriC transcription from the chromosome. A quantitative S1 nuclease assay indicated that in this mutant, the level of transcription does not fluctuate. Introduction of this mutation suppressed the growth defect of an overinitiation-type dnaAcos mutant, and severely inhibited the growth of initiation-defective dnaA mutants at semipermissive temperatures in a dnaA allele-specific manner. These results suggest that mioC-oriC transcription inhibits initiation at oriC. Indeed, flow cytometry analysis and quantification of DNA replication in synchronized cultures revealed that the mioC promoter mutation alters the control of the initiation of chromosomal replication, for instance by delaying replication within the cell cycle.


CONCLUSIONS
These results suggest that the transcriptional regulation of the mioC gene is required for cell cycle-coordinated initiation of chromosomal replication.
Su'etsugu
Masayuki
M
Department of Molecular Biology, Kyushu University Graduate School of Pharmaceutical Sciences, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
Emoto
Akiko
A
Fujimitsu
Kazuyuki
K
Keyamura
Kenji
K
Katayama
Tsutomu
T
D001425:Bacterial Outer Membrane Proteins / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D002453:Cell Cycle; D002455:Cell Division; D002876:Chromosomes, Bacterial; D004261:DNA Replication; D042522:DNA Replication Timing; D004251:DNA Transposable Elements; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology; D004926:Escherichia coli / Q000166:cytology / Q000235:genetics* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D005420:Flavoproteins / Q000096:biosynthesis / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D011401:Promoter Regions, Genetic; D012329:RNA, Bacterial / Q000096:biosynthesis; D018741:Replication Origin; D013696:Temperature; D014158:Transcription, Genetic
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D004268:DNA-Binding Proteins; C066312:DnaA protein, Bacteria; D029968:Escherichia coli Proteins; D005420:Flavoproteins; C109225:MioC protein, E coli; D012329:RNA, Bacterial; C089746:SeqA protein, E coli