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Biomedical subjects

D Baltimore

Publications and source records attributed to D Baltimore.

At least 487 records · Page 27Linked to original sources
PubMed1973

Defective interfering particles of poliovirus. IV. Mechanisms of enrichment.

Infection of HeLa cells by mixtures of standard poliovirus and defective, interfering (DI) poliovirus particles leads to a higher ratio of DI particles in the progeny than in the inoculum. The extent of this enrichment could be varied by various manipulations of the co-infected cells. At any time during the infection cycle, virions made within short times after addition of radioactive uridine were hyperenriched in DI particles; this transient hyperenrichment fell to the equilibrium enrichment level within 45 min after uridine addition. A shift of the temperature of infection from 37 to 31 C also led to a hyperenrichment of DI particles and pulse-labeling revealed a superimposed transient hyperenrichment. By contrast, cells continuously infected at 31 C showed a severe decrement in DI particles apparently because poliovirus DI particles behave as cold-sensitive mutants for RNA synthesis. Cycloheximide treatment early in the infection cycle also led to hyperenrichment. Study of the cycloheximide effect showed that the drug acted as if to change the input ratio of standard to DI particles. These effects on enrichment can be explained as aspects of two different phenomena: enrichment due to preferential DI RNA synthesis and enrichment due to preferential encapsidation of DI RNA. Both mechanisms probably play a role in the normal level of enrichment.

Carbon Radioisotopes↗
PubMed1972

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.

Adenine Nucleotides↗
PubMed1972

Covalent linkage between ribonucleic Acid primer and deoxyribonucleic Acid product of the avian myeloblastosis virus deoxyribonucleic Acid polymerase.

Initiation of deoxyribonucleic acid (DNA) synthesis by the avian myeloblastosis virus DNA polymerase was previously suggested to involve a ribonucleic acid (RNA) primer, the initial product being a DNA molecule joined by a phosphodiester bond to the RNA primer. The existence and nature of such an RNA-DNA joint was investigated by assaying for transfer of a (32)P atom from an alpha-(32)P-deoxyribonucleotide to a 2'(3')-ribonucleotide after alkaline hydrolysis of the polymerase product. Such a transfer was observed, but only from alpha-(32)P-deoxyadenosine triphosphate and only to 2'(3')-adenosine monophosphate. This same transfer was observed in both the endogenous DNA polymerase reaction of purified virions and the reconstructed reaction of purified DNA polymerase plus purified 60 to 70S viral RNA. These results indicate a high level of specificity for the initiation process and support the idea of a low-molecular-weight initiator RNA as part of the 60 to 70S RNA complex.

Journal Article↗
PubMed1971

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.

Adenine Nucleotides↗
PubMed1971

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.

Carbon Isotopes↗
PubMed1971

Ribonucleic acid polymerase in virions of Newcastle disease virus: comparison with the vesicular stomatitis virus polymerase.

The virions of Newcastle disease virus (NDV) contained an enzyme that catalyzed the incorporation of ribonucleotides into ribonucleic acid (RNA). Optimal conditions for this polymerase activity were identical to the conditions for the vesicular stomatitis virus (VSV) polymerase, and both enzymes were active for longer times at 32 C than at 37 C. However, the specific activity of the NDV polymerase was less than 3% that of the VSV polymerase. Product RNA species from the NDV and VSV polymerase reactions annealed specifically to the homologous virion RNA species. Transcriptive intermediates containing product RNA attached to the respective virion RNA could be identified in both systems.

Centrifugation, Density Gradient↗