Transcriptional control for initiation of chromosomal replication in Escherichia coli: fluctuation of the level of origin transcription ensures timely initiation

• Published in: Genes to cells : devoted to molecular & cellular mechanisms 2003-09, Vol.8 (9), p.731-745
• Main Authors: Su’etsugu, Masayuki, Emoto, Akiko, Fujimitsu, Kazuyuki, Keyamura, Kenji, Katayama, Tsutomu
• Format: Article
• Language: English
• Subjects: Bacterial Outer Membrane Proteins - physiology; Bacterial Proteins - genetics; Base Sequence; Cell Cycle; Cell Division; Chromosomes, Bacterial; DNA Replication; DNA Replication Timing; DNA Transposable Elements; DNA-Binding Proteins - genetics; DNA-Binding Proteins - physiology; Escherichia coli - cytology; Escherichia coli - genetics; Escherichia coli - metabolism; Escherichia coli Proteins - biosynthesis; Escherichia coli Proteins - genetics; Escherichia coli Proteins - physiology; Flavoproteins - biosynthesis; Flavoproteins - genetics; Molecular Sequence Data; Mutation; Promoter Regions, Genetic; Replication Origin; RNA, Bacterial - biosynthesis; Temperature; Transcription, Genetic
• ISSN: 1356-9597; 1365-2443
• DOI: 10.1046/j.1365-2443.2003.00671.x

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.