Proteins tightly associated with the termini of replicative form DNA of Kilham rat virus, an autonomous parvovirus.

Abstract

Revie et al. [Revie, D., Tseng, B. Y., Grafstrom, R. H. & Goulian, M. (1979) Proc. Nail. Acad. Sci. USA 76,[5539][5540][5541][5542][5543] have proposed that the double-stranded replicative form (RF) DNA of the autonomous rodent parvovirus H-1 has protein of 60 kDa covalently bound at its 5' termini. We present evidence that the RF DNA of a similar rodent parvovirus, Kilham rat virus (KRV), also has covalently bound protein. NaDodSO4/polyacrylamide gel electrophoresis of purified, 1251-labeled RF DNA shows that proteins of 68-72, 66, 64, and 55 kDa copurify with the DNA during velocity and equilibrium sedimentation in the presence of detergents and 4 M guanidine HCL. Phenol extraction in the presence of 2-mercaptoethanol removes the 68-to 72-kDa proteins, but the 66-, 64-, and 55-kDa proteins remain tightly, but noncovalently, bound. The latter polypeptides also appear to associate with protease-treated RF DNA when mixed with uninfected cell extract. Following removal of these proteins by electrophoresis in NaDodSO4/agarose gels, two proteins (called RF TP-90 and RF TP-40), of about 90 and 40 kDa, become evident. These remain bound to the DNA and are released only after nuclease digestion of the DNA. These two proteins, apparently not of viral origin, are associated with terminal restriction fragments of the RF DNA and appear to be covalently bound to the 5' termini of both strands.The commonly studied autonomous rodent parvoviruses [H-1, minute virus of mice (MVM), and Kilham rat virus (KRV)] have a number of properties in common. They have =5000 nucleotide-containing linear single-stranded (ss) DNA genomes with short terminal hairpins (1, 2). The DNA is packaged into an icosahedral capsid about 240 A in diameter (3)(4)(5). The viruses replicate only in host cells undergoing DNA synthesis (6) and are presumed to rely largely, if not entirely, on host factors for DNA synthesis, although no reconstituted replication system using purified proteins has been developed to demonstrate this. Because of their dependence on host S phase, autonomous parvoviruses provide a model system for studying cellular DNA replication.Following infection, the ss viral DNA is converted to a linear, double-stranded (ds) replicative form (RF) DNA molecule (7-10) by the host replicative machinery, presumably using the 3' hairpin terminus as a primer-template. This duplex RF DNA is then further replicated and acts as template for the synthesis of the viral DNA strand from a proposed unique replication origin at the 3' end of the complementary strand (11, 12). These observations have led to the proposal of a "rolling hairpin" model for parvovirus replication (13-16).Based on its aberrant electrophoretic mobility in agarose and an increase in its buoyant density in CsCl following protease treatment, most of the intracellular RF DNAs of H-1 and MVM appear to have protein covalently bound at its termini (16,17 Following the indicated labeling periods, RF DNA was purified from infected cells by a modification of the procedure of Lavelle ...

Characterization of Replicative Form DNA of the Autonomous Parvovirus Mink Enteritis Virus

“…These findings suggest the presence of a specific mechanism cleaving covalent bond between the RF DNA and the terminal protein. The terminal protein itself could play a role in this cleavage as a nickase which is one of the assumed roles of terminal protein (8,13,27).…”

“…We also designated the fragment which contains 5' terminal of vDNA as 5' terminal fragment and the fragment containing 3' terminal of vDNA as 3' terminal fragment. RF DNA with Protein It has been reported in a number of different autonomous parvoviruses that the terminal protein binds to the RF DNA at the ends (9,22,27). We examined whether the protein attaching to MEV RF DNA was also bound at the ends.…”

“…5' End of P-and F-DNA RF DNA of MVM, H-l, and KRV were bound to protein at 5' end (6,22,27). If this is the case of MEV, even after protease treatment, an amino acid or an oligopeptide attaches at 5' end of P-DNA and blocks labeling at 5' end by addition of 32P-phosphate .…”

“…It has been discussed whether the origin of terminal protein was viral or cellular (8 , 27) ; h owever, recently the protein was identified in MVM as the non-structural early protein, NSl (10). The terminal protein has been suspected to act as nickase or as protein primer of DNA replication (8,13,27), but the exact function of the protein is still unresolved. Mink enteritis virus (MEV), feline panleukopenia virus (FPLV), and canine parvovirus (CPV) are members of host-range variant species of feline parvovirus.…”

Genome Packaging Sense Is Controlled by the Efficiency of the Nick Site in the Right-End Replication Origin of Parvoviruses Minute Virus of Mice and LuIII

“…Replication assays were carried out at 37°C as previously described (7) with extracts from uninfected murine A9 cells prepared as described by Wobbe and Mitra (33). Assay mixtures (20 l) contained template plasmid DNA (10 g/ml), histidine-tagged NS1 (20 g/ml) prepared in HeLa cells from recombinant vaccinia virus and purified as described by Nuesch et al (23), deoxynucleotides, MgCl 2 , ATP, an ATP-regenerating system, and one 32 P-labeled deoxynucleoside triphosphate.…”