Correlation of gene transcription with the time of initiation of chromosome replication in Escherichia coli

Abstract

Transcriptional levels of the Escherichia coli mioC and gidA genes, which flank the chromosomal origin of replication (oriC) and the dnaA gene, were correlated with the time of initiation of chromosome replication. The transcripts were measured either in dnaC2(ts) mutants that had been aligned for initiation of chromosome replication by a temperature shift or in synchronous cultures of cells obtained using the baby machine technique. In both types of experiments, mioC transcription was inhibited prior to initiation of chromosome replication and resumed several minutes after initiation. Conversely, gidA and dnaA transcription were both inhibited after initiation of replication, coincident with the period of hemimethylation of oriC DNA. It is proposed that mioC transcription prevents initiation of chromosome replication, and must terminate before replication can begin. It is further proposed that the eclipse period between rounds of replication, i.e. the minimum interval between successive initiations, encompasses the time required to methylate GATC sequences in newly replicated oriC plus the time required to terminate mioC transcription. Conversely, the active transcription of gidA and dnaA prior to initiation is consistent with their positive effects on initiation, and their shutdown after initiation could serve to limit premature reinitiation.

Cell cycle progression in Escherichia coli B/r affects transcription of certain genes: Implications for synthetic genome design

“…In addition, we included rpoA, a gene that has been shown to not fluctuate during the cell cycle (Theisen et al, 1993). As expected, in our studies rpoA transcript levels did not fluctuate during the cell cycle (data not shown).…”

“…Previously E. coli transcript levels for several genes (most not studied here) have been shown to fluctuate with the cell replication cycle (Garrido et al, 1993;Theisen et al, 1993;Zhou and Helmstetter, 1994;Zhou et al, 1997). E. coli cultures that were synchronous with respect to either cell division or replication initiation showed that transcript levels for mnmG (gidA), mioC, dnaA, dam, ftsZ, seqA, nrdA, and mukB all decreased transiently near gene replication.…”

“…3; Theisen et al, 1993;Zhou and Helmstetter, 1994;Zhou et al, 1997). Although all studies used E. coli B/r populations synchronized by the membrane elution technique, the average doubling time and C period for the cells in previous studies were 22 and 45 min, respectively.…”

“…The increase in transcript level detected shortly after replication of each of these genes indicates that replication fork progression may affect gene transcription. Theisen et al (1993), Zhou and Helmstetter (1994) and Zhou et al (1997) for dnaA, ftsZ and nrdA, respectively. Data correlate well when plotted by C period and aligned for replication initiation.…”

Structure and Dynamics of Hemimethylated GATC Sites

“…In the process of DNA mismatch repair, the transient presence of hemimethylated GATC sites allows the repair protein MutH to specifically recognize and cleave only the newly synthesized unmethylated DNA strand (7). The transcription of genes such as dnaA2P, mioC, trpS, and trpR is induced when their promoters are transiently hemimethylated after replication (8,9). The same strategy is utilized in the transcription of certain transposons (10).…”