Resistance of adenoviral DNA replication to aphidicolin is dependent on the 72-kilodalton DNA-binding protein

African swine fever virus-induced DNA polymerase is resistant to aphidicolin

African swine fever virus (ASFV) induces the synthesis of a virus-specific DNA polymerase, which is inhibited by phosphonoacetic acid and cytosine arabinoside. In contrast to all other alpha-like DNA polymerases of DNA viruses, ASFV-specific DNA polymerase is resistant to aphidicolin. Concentrations of the drug as high as 160 microM had no effect on virus production or plaquing efficiency. The resistance of ASFV DNA polymerase to aphidicolin was confirmed by analyzing the effect of the drug on viral DNA synthesis. A moderate inhibition of viral DNA synthesis was observed when aphidicolin was added immediately after virus adsorption but normal synthesis occurred, with a peak at 10 hr p.i., when the drug was added at 2 or 4 hr p.i. This suggests that a very early phase of ASFV DNA replication is sensitive to aphidicolin and is probably catalyzed by a different enzyme. An in vitro assay of DNA polymerase activity was used to assay the sensitivity of the virus-specific DNA polymerase to inhibitors. In correspondence to the results observed in vivo, phosphonoacetic acid strongly inhibited the enzyme activity, whereas aphidicolin had no effect. Resistance to aphidicolin was independent of the concentration of dCTP used in the assay. Three independent ASFV mutants resistant to phosphonoacetic acid showed the same resistance to aphidicolin as wild type virus.

Adenovirus DNA synthesized in the presence of aphidicolin

Adenovirus types 2 and 5 DNA synthesized in vivo and in vitro in the presence of aphidicolin were studied. Inhibition of adenoviral DNA synthesis by aphidicolin was only 70% even at a concentration of 30 micrograms/ml of aphidicolin, at which the cellular DNA synthesis was completely inhibited. When initiation of the viral DNA synthesis was synchronized with hydroxyurea and labeled with [3H]thymidine for 60 min, the viral DNA synthesized in the presence of 30 micrograms/ml of aphidicolin was not of full length (35 kb) but small (approximately 12 kb) by analysis of alkaline sucrose density gradient centrifugation. When initiation of the viral DNA synthesis was not synchronized, the viral DNAs ranging from full size to 12 kb were synthesized in the presence of aphidicolin, indicating that the nascent DNAs longer than about 12 kb can continue to elongate in the presence of aphidicolin. This 12 kb DNA was not derived from the degradation products of newly synthesized full size adenoviral DNA. The viral DNA synthesis was restored and the full size of adenoviral DNA was attained within 15 min following removal of aphidicolin. About 20% of the entire viral genome length from the 5'-end was not inhibited by aphidicolin, while the synthesis of interior fragments of the adenoviral DNA was markedly inhibited by aphidicolin, judging from the electrophoretic pattern on neutral agarose gel after digestion of DNA with Hind III. These results indicate that aphidicolin inhibits adenoviral DNA replication at the internal region located approximately 20-30% from both terminals.

A fps gene without gag gene sequences transforms cells in culture and induces tumors in chickens

From molecularly cloned DNAs of Fujinami sarcoma virus (FSV) and the Schmidt-Ruppin-A strain of Rous sarcoma virus (SRA), viral DNA was constructed in which fps-specific sequences encoded in FSV replaced the src gene of SRA. A 3' fragment of FSV DNA, from an ATG methionine coding sequence 148 base pairs downstream from the gag-fps junction through the long terminal repeat, was joined to cloned SRA DNA at the translation start site for the src gene. The resultant DNA clone contained the splice acceptor site for src mRNA processing in SRA, but contained no src coding sequences from SRA nor any gag sequences from FSV. All genes for the replication of SRA were retained. Transfection of this cloned viral DNA genome into chicken embryo fibroblasts induced morphological transformation of the cells in culture. However, the morphology of the transformed cells was distinct from that observed in cells infected with wild-type FSV. The transformed cells produced a nondefective transforming virus called F36 which contained a hybrid FSV-SRA long terminal repeat. F36-infected cells produced a protein with the expected molecular weight of 91,000, which had an associated protein kinase activity and was immunoprecipitated by antibodies raised against fps gene determinants but not by antibodies raised against gag or src proteins. Injection of F36 virus into 8-day-old chicks produced tumors at the site of inoculation, detectable within 7 days. These results demonstrated that the gag portion of the gag-fps fusion protein of FSV is not required for transformation or tumorigenesis.

Effect of aphidicolin on the elongation step of adenovirus DNA replication in vitro

Adenovirus DNA synthesis carried out in vitro was inhibited by the aphidicolin. However, 30% of the DNA synthesis was resistant to aphidicolin even at a concentration of 200 micrograms/ml. When the distribution patterns of the radioactivity of the products synthesized in the presence of 50 micrograms/ml of the drug was examined after HindIII digestion of the product DNA, the radioactivity appeared preferentially in the fragments mapping nearest to the ends of the molecule. Pulse-chase experiment showed that the terminal fragments were synthesized with or without aphidicolin but that in the presence of aphidicolin the rate of elongation rapidly slowed down beyond this region, suggesting that a DNA polymerase sensitive to aphidicolin may participate in the synthesis of the internal region of adenovirus DNA.