β subunit of DNA polymerase III holoenzyme is induced upon ultraviolet irradiation or nalidixic acid treatment of Escherichia coli

Abstract

Exposure of Escherichia coli to UV irradiation or nalidixic acid, which induce both the SOS and heat shock responses, led to a 3-4-fold increase in the amount of the beta subunit of DNA polymerase III holoenzyme, as assayed by Western blot analysis using anti-beta antibodies. Such an induction was observed also in a delta rpoH mutant lacking the heat shock-specific sigma 32 subunit of RNA polymerase, but it was not observed in recA13 or lexA3 mutants, in which the SOS response cannot be induced. Mapping of transcription initiation sites of the dnaN gene, encoding the beta subunit, using the S1 nuclease protection assay showed essentially no induction of transcription upon UV irradiation, indicating that induction is regulated primarily at the post-transcriptional level. Analysis of translational gene fusions of the dnaN gene, encoding the beta subunit, to the lacZ reporter gene showed induction of beta-galactosidase activity upon UV irradiation of cells harboring the fusion plasmids. Elimination of a 5' flanking DNA sequence in which the dnaN promoters P1 and P2 were located, did not affect the UV inducibility of the gene fusions. Thus, element(s) present from P3 downstream were sufficient for the UV induction. The induction of the dnaN-lacZ gene fusions was dependent on the recA and lexA gene products, but not on the rpoH gene product, in agreement with the immunoblot analysis. The dependence of dnaN induction on the SOS regulators was not mediated via classical repression by the LexA repressor, since the dnaN promoter does not contain a sequence homologous to the LexA binding site, and dnaN mRNA was not inducible by UV light. This suggests that SOS control may be imposed indirectly, by a post-transcriptional mechanism. The increased amount of the beta subunit is needed, most likely, for increased replication and repair activities in cells which have been exposed to UV radiation.

Stationary phase induction of dnaN and recF, two genes of Escherichia coli involved in DNA replication and repair

“…The autoradiograph shown in Figure 3 also suggests that the activity of the dnaNp1 and dnaNp2 promoters is growth phase inducible and RpoS dependent. It is relevant to point out here that any growth phase effects on transcripts started at dnaNp4 might be underestimated from results such as those shown in Figure 3 since these transcripts seem to be particularly reluctant to S1 protection analysis; other authors have been unable to detect them by this method (Quiñones and Messer, 1988; Tadmor et al ., 1994).…”

“…Since re‐assembly of a processive holoenzyme should require the participation of β, coordinate induction of dnaN and recF might facilitate recovery of DNA replication at stalled replication forks. Interestingly, expression of β has been shown to be induced by DNA‐damaging agents (Kaasch et al ., 1989; Quiñones et al ., 1989; Tadmor et al ., 1994). On the other hand, there are some indications that a replication fork stalls at some frequency and disintegrates during a normal course of replication (Bierne and Michel, 1994; Canceill and Ehrlich, 1996).…”

Transcription of genes encoding DNA replication proteins is coincident with cell cycle control of DNA replication in Caulobacter crescentus

“…Most surprising was the presence of a heat shock promoter. In E. coli, at least two mechanisms, either SOS response dependent (for dnaA, dnaN, and dnaQ [43,60]) or SOS independent (dnaB [23]), appear to exist to induce expression of DNA replication genes upon detection of DNA damage. In- deed, the E. coli dnaN gene was found to encode a shorter polypeptide (␤*) whose expression is specifically induced upon UV treatment of the cells (40,55).…”

Genetic Interactions between the Escherichia coli umuDC Gene Products and the β Processivity Clamp of the Replicative DNA Polymerase

“…Following exposure of E. coli to various DNA-damaging agents, the level of transcription of the dnaN gene increases (42,60). In addition, expression of a truncated form of ␤ corresponding almost exactly to the C-terminal two-thirds of the protein is also induced (39,50).…”