scholarly journals The Second-Largest Subunit of the Mouse DNA Polymerase α-Primase Complex Facilitates Both Production and Nuclear Translocation of the Catalytic Subunit of DNA Polymerase α

1998 ◽  
Vol 18 (6) ◽  
pp. 3552-3562 ◽  
Author(s):  
Takeshi Mizuno ◽  
Nobutoshi Ito ◽  
Masayuki Yokoi ◽  
Akio Kobayashi ◽  
Katsuyuki Tamai ◽  
...  
Keyword(s):  
Dna Polymerase ◽  
Mammalian Cells ◽  
Nuclear Translocation ◽  
Expression System ◽  
Physiological Role ◽  
Polymerase Activity ◽  
Catalytic Subunit ◽  
Dna Polymerase Α ◽  
Localization Signal ◽  
Primase Complex

ABSTRACT DNA polymerase α-primase is a replication enzyme necessary for DNA replication in all eukaryotes examined so far. Mouse DNA polymerase α is made up of four subunits, the largest of which is the catalytic subunit with a molecular mass of 180 kDa (p180). This subunit exists as a tight complex with the second-largest subunit (p68), whose physiological role has remained unclear up until now. We set out to characterize these subunits individually or in combination by using a cDNA expression system in cultured mammalian cells. Coexpression of p68 markedly increased the protein level of p180, with the result that ectopically generated DNA polymerase activity was dramatically increased. Immunofluorescence analysis showed that while either singly expressed p180 or p68 was localized in the cytoplasm, cotransfection of both subunits resulted in colocalization in the nucleus. We identified a putative nuclear localization signal for p180 (residues 1419 to 1437) and found that interaction with p68 is essential for p180 to translocate into the nucleus. These results indicate that association of p180 with p68 is important for both protein synthesis of p180 and translocation into the nucleus, implying that p68 plays a pivotal role in the newly synthesized DNA polymerase α complex.

scholarly journals Identification of the nuclear localization signal of mouse DNA primase: nuclear transport of p46 subunit is facilitated by interaction with p54 subunit

1996 ◽  
Vol 109 (11) ◽  
pp. 2627-2636 ◽  
Author(s):  
T. Mizuno ◽  
T. Okamoto ◽  
M. Yokoi ◽  
M. Izumi ◽  
A. Kobayashi ◽  
...  
Keyword(s):  
Dna Polymerase ◽  
Nuclear Localization ◽  
Nuclear Localization Signal ◽  
Subcellular Distribution ◽  
Nuclear Translocation ◽  
Expression System ◽  
Physiological Role ◽  
Dna Polymerase Alpha ◽  
Dna Primase ◽  
Localization Signal

DNA polymerase alpha-primase is a replication enzyme necessary for DNA replication in all eukaryotes. Mouse DNA primase is composed of two subunits: a 46 kDa protein (p46), which is the catalytic subunit capable of RNA primer synthesis, and a 54 kDa protein (p54), whose physiological role is not clear. To understand the structure-function relationship of DNA primase, we set out to characterize these two subunits individually or in combination using a cDNA expression system in mammalian cultured cells, and determined the subcellular distribution of ectopically expressed DNA primase. The p54 expressed in COS-1 cells after transfection was predominantly localized in the nucleus, whereas p46 was retained in the cytoplasm as shown by indirect immunofluorescence analysis. Using several mutant proteins with deletions or substitutions as well as chimeric constructs, we identified the nuclear localization signal of p54 as RIRKKLR, encoded near the amino terminus (residues 6–12). Furthermore, co-expression of both p46 and p54 subunits markedly altered the subcellular distribution of p46; co-expressed p46 was transported into the nucleus as efficiently as p54. These results demonstrate that p54 has a nuclear localization signal and is able to be translocated into the nucleus independently of DNA polymerase alpha subunits. In contrast, p46 lacks a nuclear localization signal, and its nuclear translocation is facilitated by interaction with p54. We present here first evidence for a novel role of p54 in the nuclear translocation process, and a piggy-back binding transport mechanism of mouse DNA primase.

scholarly journals Molecular Architecture of the Mouse DNA Polymerase α-Primase Complex

1999 ◽  
Vol 19 (11) ◽  
pp. 7886-7896 ◽  
Author(s):  
Takeshi Mizuno ◽  
Kumiko Yamagishi ◽  
Hiroshi Miyazawa ◽  
Fumio Hanaoka
Keyword(s):  
Dna Polymerase ◽  
Polymerase Activity ◽  
Terminal Region ◽  
Subunit Assembly ◽  
Dna Polymerase Α ◽  
Amino Terminal ◽  
Terminal Domain ◽  
Carboxyl Terminal ◽  
Dna Primers ◽  
Primase Complex

ABSTRACT The DNA polymerase α-primase complex is the only enzyme that provides RNA-DNA primers for chromosomal DNA replication in eukaryotes. Mouse DNA polymerase α has been shown to consist of four subunits, p180, p68, p54, and p46. To characterize the domain structures and subunit requirements for the assembly of the complex, we constructed eukaryotic polycistronic cDNA expression plasmids expressing pairwise the four subunits of DNA polymerase α. In addition, the constructs contained an internal ribosome entry site derived from poliovirus. The constructs were transfected in different combinations with vectors expressing single subunits to allow the simultaneous expression of three or four of the subunits in cultured mammalian cells. We demonstrate that the carboxyl-terminal region of p180 (residues 1235 to 1465) is essential for its interaction with both p68 and p54-p46 by immunohistochemical analysis and coprecipitation studies with antibodies. Mutations in the putative zinc fingers present in the carboxyl terminus of p180 abolished the interaction with p68 completely, although the mutants were still capable of interacting with p54-p46. Furthermore, the amino-terminal region (residues 1 to 329) and the carboxyl-terminal region (residues 1280 to 1465) were revealed to be dispensable for DNA polymerase activity. Thus, we can divide the p180 subunit into three domains. The first is the amino-terminal domain (residues 1 to 329), which is dispensable for both polymerase activity and subunit assembly. The second is the minimal core domain (residues 330 to 1279), required for polymerase activity. The third is the carboxyl-terminal domain (residues 1280 to 1465), which is dispensable for polymerase activity but required for the interaction with the other three subunits. Taken together, these results allow us to propose the first structural model for the DNA polymerase α-primase complex in terms of subunit assembly, domain structure, and stepwise formation at the cellular level.

scholarly journals The Saccharomyces telomere-binding protein Cdc13p interacts with both the catalytic subunit of DNA polymerase α and the telomerase-associated Est1 protein

2000 ◽  
Vol 14 (14) ◽  
pp. 1777-1788 ◽  
Author(s):  
Haiyan Qi ◽  
Virginia A. Zakian
Keyword(s):  
Dna Polymerase ◽  
Binding Protein ◽  
Point Mutations ◽  
Single Strand ◽  
Catalytic Subunit ◽  
Full Length ◽  
Temperature Sensitive ◽  
Dna Polymerase Α ◽  
Telomere Binding Protein

Saccharomyces telomeres consist of ∼350 bp of C1-3A/TG1-3 DNA. Most of this ∼350 bp is replicated by standard, semiconservative DNA replication. After conventional replication, the C1-3A strand is degraded to generate a long single strand TG1-3 tail that can serve as a substrate for telomerase. Cdc13p is a single strand TG1-3DNA-binding protein that localizes to telomeres in vivo. Genetic data suggest that the Cdc13p has multiple roles in telomere replication. We used two hybrid analysis to demonstrate that Cdc13p interacted with both the catalytic subunit of DNA polymerase α, Pol1p, and the telomerase RNA-associated protein, Est1p. The association of these proteins was confirmed by biochemical analysis using full-length or nearly full-length proteins. Point mutations in either CDC13 orPOL1 that reduced the Cdc13p–Pol1p interaction resulted in telomerase mediated telomere lengthening. Over–expression of the carboxyl terminus of Est1p partially suppressed the temperature sensitive lethality of a cdc13-1 strain. We propose that Cdc13p's interaction with Est1p promotes TG1-3 strand lengthening by telomerase and its interaction with Pol1p promotes C1-3A strand resynthesis by DNA polymerase α.

scholarly journals Molecular cloning of the cDNA for the catalytic subunit of plant DNA polymerase α and its cell-cycle dependent expression

1997 ◽  
Vol 2 (11) ◽  
pp. 695-709 ◽  
Author(s):  
Masayuki Yokoi ◽  
Masaki Ito ◽  
Masako Izumi ◽  
Hiroshi Miyazawa ◽  
Hirokazu Nakai ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Molecular Cloning ◽  
Dna Polymerase ◽  
Catalytic Subunit ◽  
Dna Polymerase Α ◽  
Plant Dna ◽  
Cycle Dependent
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