Absence of polymerase protein in virions of alpha-type rous sarcoma virus.

Noninfectious particles of a mutant of Rous sarcoma virus failed to exhibit DNA polymerase activity even with the use of the most sensitive synthetic template-primer complexes. A neutralization blocking test against antibody to DNA polymerase revealed that these mutants did not contain protein immunologically related to the DNA polymerase.

Primer requirement and template specificity of the DNA polymerase of RNA tumor viruses.

Polyribonucleotides will act as efficient templates for the DNA polymerases found in the virions of avian myeloblastosis virus and mouse leukemia virus if a short complementary oligodeoxyribonucleotide primer is added. Synthesis of the complementary polydeoxyribonucleotide continues until an amount of polymer equal to the amount of initial template has been produced. The two viruses show slightly different specificities toward the four homoribopolymers. Polydeoxyribonucleotides are generally much poorer templates than the homologous polyribonucleotides, in most cases yielding no detectable synthesis. The DNA polymerase of RNA tumor viruses, therefore, have the same requirements for activity as do other DNA polymerases, except that they prefer polyribonucleotides over polydeoxyribonucleotides as templates.

Terminal deoxynucleotidyl transferase in a case of childhood acute lymphoblastic leukemia.

Cells from a patient with childhood acute lymphoblastic leukemia contain an apparent DNA polymerase activity that was not found in any other cells except thymus cells. The enzyme has the properties of terminal transferase, an enzyme known to be found in thymocytes. The cells also contain the three major DNA polymerases found in growing cells. The results suggest that these tumor cells arose from a block in the differentiation of thymocytes. Terminal transferase may be a marker for the origin of leukemic cells.

Defective interfering particles of poliovirus. I. Isolation and physical properties.

A class of defective interfering (DI) poliovirus particles has been identified. The first was found as a contaminant of a viral stock; others have been isolated by serial passage at a high multiplicity of infection. The DI particles are less dense than standard virus and sediment more slowly. Their ribonucleic acid (RNA) sediments more slowly than standard RNA and has a higher electrophoretic mobility. Competition hybridization experiments with double-stranded viral RNA indicate that DI RNA is 80 to 90% of the length of standard RNA. The proteins of DI particles are indistinguishable from those of standard poliovirus.

Forms of deoxyribonucleic acid produced by virions of the ribonucleic acid tumor viruses.

The in vitro product of mouse leukemia virus deoxyribonucleic acid (DNA) polymerase can be separated into two fractions by sedimentation in sucrose gradients. These two fractions were analyzed for their content of single-stranded DNA, double-stranded DNA, and DNA-ribonucleic acid (RNA) hybrid by (i) digestion with enzymes of known specificity and (ii) equilibrium centrifugation in Cs(2)SO(4) gradients. The major fraction early in the reaction contained equal amounts of single-stranded DNA and DNA-RNA hybrid and little double-stranded DNA. The major fraction after extensive synthesis contained equal amounts of single-and double-stranded DNA and little hybrid. In the presence of actinomycin D, the predominant product was single-stranded DNA. To account for these various forms of DNA, we postulate the following model: the first DNA synthesis occurs in a replicative complex containing growing DNA molecules attached to an RNA molecule. Each DNA molecule is displaced as single-stranded DNA by the synthesis of the following DNA strand, and the single-stranded DNA is copied to form double-stranded DNA either before or after release of the single strand from the RNA. Actinomycin blocks this conversion of single-to double-stranded DNA.