GENE-TRANSCRIPTION AND CHROMOSOME-REPLICATION IN ESCHERICHIA-COLI

Transcript levels of several Escherichia coil genes involved in chromo some replication and cell division were measured in dnaC2(Ts) mutants synchronized for chromosome replication by temperature shifts. Levels of transcripts from four of the genes, dam, nrdA, mukB, and seqA, were reduced at a certain stage during chromosome replication, The magnitu des of the decreases were similar to those reported previously for fts Q and ftsZ (P. Zhou and C. E. Helmstetter, J. Bacteriol. 176:6100-6106 , 1994) but considerably less than those seen with dnaA, gidA, and mio C (P. W. Theisen, J. E. Grimwade, A. C. Leonard, J. A. Began, and C. E . Helmstetter, Mol. Microbiol. 10:575-583, 1993). The decreases in tra nscripts appeared to correlate with the estimated time at which the ge nes replicated. This same conclusion was reached in studies with synch ronous cultures obtained with the baby machine in those instances in w hich periodicities in transcript levels were clearly evident. The tran scriptional levels for two genes, minE and hrs, did not fluctuate sign ificantly, whereas the transcripts for one gene, iciA, appeared to inc rease transiently. The results support the idea that cell cycle timing in E. coli is not governed by timed bursts of gene expression, since the overall findings summarized in this report are generally consisten t with cell cycle-dependent transient inhibitions of transcription rat her than stimulations.