Incorporation of Precursors into Ribonucleic Acid, Protein, Glycoprotein, and Lipoprotein of Avian Myeloblastosis Virions

Abstract

Freshly explanted leukemic myeloblasts produce avian myeloblastosis virus (AMV) at a constant rate without any obvious cytopathic effect; therefore, subviral components are continually synthesized at a steady rate. The incorporation of various radioactive precursors into virions was monitored by determination of radioactivity in purified virus after density equilibrium sedimentation in preformed sucrose gradients. The kinetics of incorporation of 3H-uridine have shown that there is an average time interval of 3 to 4 hr (half-life) between the time viral ribonucleic acid (RNA) is synthesized and the time it is released as a mature virus particle; this represents the average time interval spent by AMV-RNA in an intracellular pool. Studies with '4C-phenylalanine have revealed that some protein synthesis takes place at or near the cell surface immediately prior to maturation and release of virus. "4C-glucosamine also appears to be incorporated into the outer viral envelope shortly before maturation. On the other hand, there is an average lag of about 16 to 20 hr before '4C-ethanolamine incorporated into intracellular lipoprotein appears in free virions; this probably reflects the kinetics of replacement of cellular surface membrane. Actinomycin D inhibits AMV-RNA within 30 min but permits the maturation of AMV to continue for at least 2 hr. AMV released in the presence of actinomycin D contains AMV-RNA synthesized before the addition of the drug.

Mitosis is required for production of murine leukemia virus and structural proteins during de novo infection

“…Secondly, the time of virus protein production and the appearance of infectious virus indicated that the interval between the manufacture of these three structural proteins and their incorporation into infectious virus must be quite short. This is also in agreement with the timing of avian oncornavirus production in the presence of some inhibitors of macromolecular synthesis (1).…”

“…DNA synthesis was performed in petri dishes of both depleted normal and MLV-infected cells. The rate of uptake of [3 H]thymidine (New England Nuclear Corp.), 1 MCi/dish in 1 ml, was measured as the counts per minute of precursor rendered acid insoluble after 1 h of incubation at 37 C, and expressed as activity/105 cells (5). Cells in mitosis were counted in sparsely seeded cultures.…”

Deficiency of 60 to 70 S RNA in Murine Leukemia Virus Particles Assembled in Cells Treated with Actinomycin D

“…macromolecules (3,6) and suggest that these molecules can be utilized for terminal steps in assembly under conditions of severely restricted viral RNA synthesis.…”

New directions in genetics utilizing tissue culture techniques1

“…In tissue culture it was demonstrated that when a cell was infected with an RNA tumor virus, the Rous sarcoma virus, the characteristic changes produced in the cell by the virus could be inhibited by inhibiting DNA synthesis (TEMIN 1968). Also it was demonstrated in tissue culture that the production of RNA tumor viruses are sensitive to actinomycin D (TEMIN 1963;BALUDA and NAYAK 1969), a substance which inhibits transcription of DNA; and finally, cells transformed in culture by RNA tumor viruses contain new DNA which hybridizes with viral RNA (TEMIN 1964). It was these tissue culture experiments that led Temin and Baltimore to their very fine observations in the cell free system.…”