Primer requirement and template specificity of a DNA polymerase of chick embryo

A DNA polymerase purified from extracts of chick embryo catalyzes the synthesis of poly(dT) in the presence of poly(rA) or poly(dA) as template and poly(dT) or oligo(dT) as primer. Oligo- or polyribonucleotides are relatively ineffective initiators of polydeoxynucleotide polymerization. Using activated DNA as template, the enzyme catalyzes a repair-like reaction that resembles that catalyzed by RNA-directed DNA polymerase of RNA tumor viruses and Escherichia coli DNA polymerase II. With natural templates containing poly(rA) sequences, such as avian myeloblastosis virus RNA or rabbit globin mRNA, and oligo(dT) as initiator, principally poly(dT) is synthesized. Consequently, the enzyme differs from the RNA-directed DNA polymerase associated with RNA tumor viruses by its incapacity to transcribe heteropolymeric regions of RNA templates. The possible role of the enzyme in repair of DNA during transcription is discussed.

Yellow fever vaccination, avian leukosis virus, and cancer risk in man

Comparison was made between 2659 veterans who died of cancer, during 1950 to 1954 or 1959 to 1963, and matched controls, based on the frequency of yellow fever immunization during World War II. The vaccine was produced from chick embryos that almost certainly contained avian leukosis-sarcoma viruses. Among the veterans, no relation was found between vaccination and leukemia, lymphoma, or other cancer.

Endogenous RNA-directed DNA polymerase activity in uninfected chicken embryos

Early chicken embryos that are either positive or negative for group-specific antigens of avian leukosis viruses contained endogenous RNA-directed DNA polymerase activity. This endogenous DNA polymerase activity was not increased after mixture of soluble DNA polymerases isolated from chicken embryos with disrupted chicken embryo cells. The endogenous activity was resistant to treatment with deoxyribonuclease, and the initial rate of DNA synthesis was partially resistant to actinomycin D. In contrast, over 90% of the endogenous polymerase activity was destroyed by ribonuclease in medium with high salt concentration. The DNA product of the endogenous DNA polymerase activity from chicken embryos did not hybridize with RNA of Rous sarcoma virus or reticuloendotheliosis virus, whereas about 40% of this DNA product hybridized with the RNA from the same chicken-cell fraction. Antibody against DNA polymerase of avian myeloblastosis virus did not neutralize the chicken endogenous DNA polymerase activity. These results demonstrate that uninfected chicken embryo cells contain endogenous RNA-directed DNA polymerase activity that is not derived from avian leukosis or reticuloendotheliosis viruses.

Purification and immunological characterization of the major internal protein of the RD-114 virus

The major internal protein of the RD-114 virus that appeared in a human tumor cell line, RD, after passage through fetal cats was purified by isoelectric focusing and used to prepare antibody in guinea pigs. The protein has a molecular weight of 33,500 in sodium dodecyl sulfate-polyacrylamide gels, and an isoelectric point of 9.1. This contrasts with a molecular weight of 25,000 and an isoelectric point of 8.3 obtained previously for the major protein of cat C-type viruses. The RD-114 protein carries determinants common to all mammalian C-type viruses but not species-specific determinants of cat, mouse, rat, hamster, chicken, and Russell's viper C-type viruses. In addition, two other proteins found in cat virus preparations were not detected in the RD-114 virus. Antiserum to the RD-114 viral protein proved highly specific by complement fixation and gel diffusion assays, and, in addition to the above mentioned mammalian viruses, the antiserum did not react with concentrates of the Woolly monkey or Gibbon ape C-type viruses. These data support the conclusion that the RD-114 virus is a human virus activated by passage through fetal cats. Until additional isolates are made from human cells, the identity of the RD-114 virus as a human C-type tumor virus cannot be fully established; however, this would be highly probable if the species-specific group-specific antigen of RD-114 could be demonstrated in human tumor and/or embryonic tissues.