scholarly journals Role of the Hydrophilic Channels of Simian Virus 40 T-Antigen Helicase in DNA Replication

2007 ◽  
Vol 81 (9) ◽  
pp. 4510-4519 ◽  
Author(s):  
Weiping Wang ◽  
David Manna ◽  
Daniel T. Simmons
Keyword(s):  
Dna Replication ◽  
Dna Binding ◽  
Single Point ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Single Stranded Dna ◽  
Low Protein ◽  
Class C ◽  
Sv40 Dna

ABSTRACT The simian virus 40 (SV40) hexameric helicase consists of a central channel and six hydrophilic channels located between adjacent large tier domains within each hexamer. To study the function of the hydrophilic channels in SV40 DNA replication, a series of single-point substitutions were introduced at sites not directly involved in protein-protein contacts. The mutants were characterized biochemically in various ways. All mutants oligomerized normally in the absence of DNA. Interestingly, 8 of the 10 mutants failed to unwind an origin-containing DNA fragment and nine of them were totally unable to support SV40 DNA replication in vitro. The mutants fell into four classes based on their biochemical properties. Class A mutants bound DNA normally and had normal ATPase and helicase activities but failed to unwind origin DNA and support SV40 DNA replication. Class B mutants were compromised in single-stranded DNA and origin DNA binding at low protein concentrations. They were defective in helicase activity and unwinding of the origin and in supporting DNA replication. Class C and D mutants possessed higher-than-normal single-stranded DNA binding activity at low protein concentrations. The class C mutants failed to separate origin DNA and support DNA replication. The class D mutants unwound origin DNA normally but were compromised in their ability to support DNA replication. Taken together, these results suggest that the hydrophilic channels have an active role in the unwinding of SV40 DNA from the origin and the placement of the resulting single strands within the helicase.

scholarly journals Role of Single-Stranded DNA Binding Activity of T Antigen in Simian Virus 40 DNA Replication

2001 ◽  
Vol 75 (6) ◽  
pp. 2839-2847 ◽  
Author(s):  
Chunxiao Wu ◽  
Rupa Roy ◽  
Daniel T. Simmons
Keyword(s):  
Dna Replication ◽  
Dna Binding ◽  
Single Point ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
Binding Activity ◽  
T Antigen ◽  
Amino Acid Residues ◽  
Single Stranded Dna ◽  
Dna Binding Activity

ABSTRACT We have previously mapped the single-stranded DNA binding domain of large T antigen to amino acid residues 259 to 627. By using internal deletion mutants, we show that this domain most likely begins after residue 301 and that the region between residues 501 and 550 is not required. To study the function of this binding activity, a series of single-point substitutions were introduced in this domain, and the mutants were tested for their ability to support simian virus 40 (SV40) replication and to bind to single-stranded DNA. Two replication-defective mutants (429DA and 460EA) were grossly impaired in single-stranded DNA binding. These two mutants were further tested for other biochemical activities needed for viral DNA replication. They bound to origin DNA and formed double hexamers in the presence of ATP. Their ability to unwind origin DNA and a helicase substrate was severely reduced, although they still had ATPase activity. These results suggest that the single-stranded DNA binding activity is involved in DNA unwinding. The two mutants were also very defective in structural distortion of origin DNA, making it likely that single-stranded DNA binding is also required for this process. These data show that single-stranded DNA binding is needed for at least two steps during SV40 DNA replication.

Simian virus 40 origin- and T-antigen-dependent DNA replication with Drosophila factors in vitro

1994 ◽  
Vol 14 (8) ◽  
pp. 5114-5122
Author(s):  
R T Kamakaka ◽  
P D Kaufman ◽  
B Stillman ◽  
P G Mitsis ◽  
J T Kadonaga
Keyword(s):  
Dna Replication ◽  
Dna Binding ◽  
Binding Protein ◽  
Simian Virus 40 ◽  
Dna Binding Protein ◽  
Simian Virus ◽  
T Antigen ◽  
Drosophila Species ◽  
Single Stranded Dna ◽  
Sv40 Dna

DNA replication of double-stranded simian virus 40 (SV40) origin-containing plasmids, which has been previously thought to be a species-specific process that occurs only with factors derived from primate cells, is catalyzed with an extract derived from embryos of the fruit fly Drosophila melanogaster. This reaction is dependent upon both large T antigen, the SV40-encoded replication initiator protein and DNA helicase, and a functional T-antigen binding site at the origin of DNA replication. The efficiency of replication with extracts derived from Drosophila embryos is approximately 10% of that observed with extracts prepared from human 293 cells. This activity is not a unique property of embryonic extracts, as cytoplasmic extracts from Drosophila tissue culture cells also support T-antigen-mediated replication of SV40 DNA. By using highly purified proteins, DNA synthesis is initiated by Drosophila polymerase alpha-primase in a T-antigen-dependent manner in the presence of Drosophila replication protein A (RP-A; also known as single-stranded DNA-binding protein), but neither human RP-A nor Escherichia coli single-stranded DNA-binding protein could substitute for Drosophila RP-A. In reciprocal experiments, however, Drosophila RP-A was able to substitute for human RP-A in reactions carried out with human polymerase alpha-primase. These results collectively indicate that many of the specific functional interactions among T antigen, polymerase alpha-primase, and RP-A are conserved from primates to Drosophila species. Moreover, the observation that SV40 DNA replication can be performed with Drosophila factors provides a useful assay for the study of bidirectional DNA replication in Drosophila species in the context of a complete replication reaction.

scholarly journals Simian virus 40 origin- and T-antigen-dependent DNA replication with Drosophila factors in vitro.

1994 ◽  
Vol 14 (8) ◽  
pp. 5114-5122 ◽  
Author(s):  
R T Kamakaka ◽  
P D Kaufman ◽  
B Stillman ◽  
P G Mitsis ◽  
J T Kadonaga
Keyword(s):  
Dna Replication ◽  
Dna Binding ◽  
Binding Protein ◽  
Simian Virus 40 ◽  
Dna Binding Protein ◽  
Simian Virus ◽  
T Antigen ◽  
Drosophila Species ◽  
Single Stranded Dna ◽  
Sv40 Dna

DNA replication of double-stranded simian virus 40 (SV40) origin-containing plasmids, which has been previously thought to be a species-specific process that occurs only with factors derived from primate cells, is catalyzed with an extract derived from embryos of the fruit fly Drosophila melanogaster. This reaction is dependent upon both large T antigen, the SV40-encoded replication initiator protein and DNA helicase, and a functional T-antigen binding site at the origin of DNA replication. The efficiency of replication with extracts derived from Drosophila embryos is approximately 10% of that observed with extracts prepared from human 293 cells. This activity is not a unique property of embryonic extracts, as cytoplasmic extracts from Drosophila tissue culture cells also support T-antigen-mediated replication of SV40 DNA. By using highly purified proteins, DNA synthesis is initiated by Drosophila polymerase alpha-primase in a T-antigen-dependent manner in the presence of Drosophila replication protein A (RP-A; also known as single-stranded DNA-binding protein), but neither human RP-A nor Escherichia coli single-stranded DNA-binding protein could substitute for Drosophila RP-A. In reciprocal experiments, however, Drosophila RP-A was able to substitute for human RP-A in reactions carried out with human polymerase alpha-primase. These results collectively indicate that many of the specific functional interactions among T antigen, polymerase alpha-primase, and RP-A are conserved from primates to Drosophila species. Moreover, the observation that SV40 DNA replication can be performed with Drosophila factors provides a useful assay for the study of bidirectional DNA replication in Drosophila species in the context of a complete replication reaction.

Replication of cloned DNA containing the Alu family sequence during cell extract-promoting simian virus 40 DNA synthesis

1984 ◽  
Vol 4 (8) ◽  
pp. 1476-1482
Author(s):  
H Ariga
Keyword(s):  
Dna Replication ◽  
Dna Synthesis ◽  
Rna Polymerase Iii ◽  
Simian Virus 40 ◽  
Cell Extract ◽  
Simian Virus ◽  
T Antigen ◽  
Sv40 T Antigen ◽  
Sv40 Dna

The replicating activity of several cloned DNAs containing putative origin sequences was examined in a cell-free extract that absolutely depends on simian virus 40 (SV40) T antigen promoting initiation of SV40 DNA replication in vitro. Of the three DNAs containing the human Alu family sequence (BLUR8), the origin of (Saccharomyces cerevisiae plasmid 2 micron DNA (pJD29), and the yeast autonomous replicating sequence (YRp7), only BLUR8 was active as a template. Replication in a reaction mixture with BLUR8 as a template was semiconservative and not primed by a putative RNA polymerase III transcript synthesized on the Alu family sequence in vitro. Pulse-chase experiments showed that the small-sized DNA produced in a short-term incubation was converted to full-length closed circular and open circular DNAs in alkaline sucrose gradients. DNA synthesis in extracts began in a region of the Alu family sequence and was inhibited 80% by the addition of anti-T serum. Furthermore, partially purified T antigen bound the Alu family sequence in BLUR8 by the DNA-binding immunoassay. These results suggest that SV40 T antigen recognizes the Alu family sequence, similar to the origin sequence of SV40 DNA, and initiates semiconservative DNA replication in vitro.

Binding properties of replication protein A from human and yeast cells

1992 ◽  
Vol 12 (7) ◽  
pp. 3050-3059 ◽  
Author(s):  
C Kim ◽  
R O Snyder ◽  
M S Wold
Keyword(s):  
Dna Replication ◽  
Dna Binding ◽  
Protein A ◽  
Simian Virus 40 ◽  
Replication Protein A ◽  
Simian Virus ◽  
Yeast Cells ◽  
Origin Of Replication ◽  
Binding Properties ◽  
Single Stranded Dna

Replication protein A (RP-A; also known as replication factor A and human SSB), is a single-stranded DNA-binding protein that is required for simian virus 40 DNA replication in vitro. RP-A isolated from both human and yeast cells is a very stable complex composed of 3 subunits (70, 32, and 14 kDa). We have analyzed the DNA-binding properties of both human and yeast RP-A in order to gain a better understanding of their role(s) in DNA replication. Human RP-A has high affinity for single-stranded DNA and low affinity for RNA and double-stranded DNA. The apparent affinity constant of RP-A for single-stranded DNA is in the range of 10(9) M-1. RP-A has a binding site size of approximately 30 nucleotides and does not bind cooperatively. The binding of RP-A to single-stranded DNA is partially sequence dependent. The affinity of human RP-A for pyrimidines is approximately 50-fold higher than its affinity for purines. The binding properties of yeast RP-A are similar to those of the human protein. Both yeast and human RP-A bind preferentially to the pyrimidine-rich strand of a homologous origin of replication: the ARS307 or the simian virus 40 origin of replication, respectively. This asymmetric binding suggests that RP-A could play a direct role in the process of initiation of DNA replication.

scholarly journals Different oligomeric forms of protein phosphatase 2A activate and inhibit simian virus 40 DNA replication

1994 ◽  
Vol 14 (7) ◽  
pp. 4616-4623
Author(s):  
A Cegielska ◽  
S Shaffer ◽  
R Derua ◽  
J Goris ◽  
D M Virshup
Keyword(s):  
Dna Replication ◽  
Protein Phosphatase ◽  
Protein Phosphatase 2A ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Catalytic Subunit ◽  
B Subunit ◽  
Phosphatase 2A ◽  
Sv40 Dna

The ability of simian virus 40 (SV40) large T antigen to catalyze the initiation of viral DNA replication is regulated by its phosphorylation state. Previous studies have identified the free catalytic subunit of protein phosphatase 2A (PP2Ac) as the cellular phosphatase which can remove inhibitory phosphoryl groups from serines 120 and 123. The catalytic C subunit exists in the cell complexed with a 65-kDa A subunit and one of several B subunits. To determine if any of the holoenzymes could activate T antigen, we tested the ability of the heterodimeric AC and two heterotrimeric ABC forms to stimulate T-antigen function in unwinding the origin of SV40 DNA replication. Only free catalytic subunit C and the heterotrimeric form with a 72-kDa B subunit (PP2A-T72) could stimulate T-antigen-dependent origin unwinding. Both the dimeric form (PP2A-D) and the heterotrimer with a 55-kDa B subunit (PP2A-T55) actively inhibited T-antigen function. We found that PP2A-T72 activated T antigen by dephosphorylating serines 120 and 123, while PP2A-D and PP2A-T55 inactivated T antigen by dephosphorylating the p34cdc2 target site, threonine 124. Thus, alterations in the subunit composition of PP2A holoenzymes have significant functional consequences for the initiation of in vitro SV40 DNA replication. The regulatory B subunits of PP2A may play a role in regulating SV40 DNA replication in infected cells as well.

scholarly journals Primer-DNA formation during simian virus 40 DNA replication in vitro.

1993 ◽  
Vol 13 (5) ◽  
pp. 2882-2890 ◽  
Author(s):  
D Denis ◽  
P A Bullock
Keyword(s):  
Dna Replication ◽  
Proliferating Cell Nuclear Antigen ◽  
Simian Virus 40 ◽  
Simian Virus ◽  
T Antigen ◽  
Nuclear Antigen ◽  
Origin Region ◽  
Sv40 Dna ◽  
Proliferating Cell

Studies of simian virus 40 (SV40) DNA replication in vitro have identified a small (approximately 30-nucleotide) RNA-DNA hybrid species termed primer-DNA. Initial experiments indicated that T antigen and the polymerase alpha-primase complex are required to form primer-DNA. Proliferating cell nuclear antigen, and presumably proliferating cell nuclear antigen-dependent polymerases, is not needed to form this species. Herein, we present an investigation of the stages at which primer-DNA functions during SV40 DNA replication in vitro. Hybridization studies indicate that primer-DNA is initially formed in the origin region and is subsequently synthesized in regions distal to the origin. At all time points, primer-DNA is synthesized from templates for lagging-strand DNA replication. These studies indicate that primer-DNA functions during both initiation and elongation stages of SV40 DNA synthesis. Results of additional experiments suggesting a precursor-product relationship between formation of primer-DNA and Okazaki fragments are presented.

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