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E2F regulates growth-dependent transcription of genes encoding both catalytic and regulatory subunits of mouse
N Nishikawa1, M Izumi, M Yokoi
1Cellular Physiology Laboratory, RIKEN (The Institute of Physical and Chemical Research), Wako, Saitama 351-0198, Japan.
Abstract:
DNA polymerase alpha-primase is one of the principal enzymes involved in eukaryotic chromosomal DNA replication. Mouse DNA polymerase alpha-primase consists of four subunits with molecular masses of 180, 68, 54 and 46 kDa. Protein and mRNA expression levels of the four subunits are up-regulated in a coordinated manner in response to growth stimulation. We have previously analysed the transcription of the 180 kDa (p180) and 68 kDa (p68) subunits, which form the DNA polymerase catalytic complex, and found that growth-dependent regulation of transcription of the mouse p180 and p68 genes is mediated by a common factor, E2F, while the basal transcription of the genes is regulated by different transcription factors. We characterized the transcriptional regulation of the 54 kDa (p54) and 46 kDa (p46) subunits, which form the DNA primase catalytic complex. We isolated genomic clones spanning the 5'-flanking regions of the p54 and p46 genes and showed, using transient expression and gel mobility shift assays, that the basal transcription of p54 is controlled by Sp1 and GA-binding protein, as is the basal transcription of the p180 gene. The basal transcription of p46 is controlled by unknown factor(s) which were bound to the upstream sequence. The variant E2F sites close to the transcription initiation sites of the p54 and p46 genes had no basal promoter activity, but were essential for the growth-dependent transcription of both genes. The promoter regions of the four subunits of mouse DNA polymerase d-primase complex share several common features. The coordinated transcription of all four subunits in response to growth stimulation appears to be controlled by E2F.
Insights
Growth stimulation coordinates mouse DNA polymerase alpha-primase subunit transcription via E2F. This key enzyme complex
Area of Science:
- Molecular Biology
- Genetics
- Biochemistry
Background:
- DNA polymerase alpha-primase is crucial for eukaryotic DNA replication.
- It comprises four subunits (180, 68, 54, 46 kDa) whose expression is coordinated with cell growth.
- Previous studies analyzed the p180 and p68 subunits' transcription.
Purpose of the Study:
- To characterize the transcriptional regulation of the p54 and p46 subunits of mouse DNA polymerase alpha-primase.
- To identify transcription factors controlling basal and growth-dependent expression of these subunits.
- To understand the coordinated regulation of all four subunits.
Main Methods:
- Isolation of genomic clones for p54 and p46 5'-flanking regions.
- Transient expression assays.
- Gel mobility shift assays.
Main Results:
- Basal transcription of p54 is regulated by Sp1 and GA-binding protein, similar to p180.
- Basal transcription of p46 is regulated by unknown factors.
- Variant E2F sites are essential for growth-dependent transcription of p54 and p46.
- Common features exist in the promoter regions of all four subunits.
Conclusions:
- Coordinated transcription of all four DNA polymerase alpha-primase subunits in response to growth stimulation is primarily controlled by E2F.
- Distinct factors regulate basal transcription of different subunits.
- E2F plays a critical role in linking cell growth signals to DNA replication machinery.