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

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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 ribo-nucleic 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 14C-phenylalanine have revealed that some protein synthesis takes place at or near the cell surface immediately prior to maturation and release of virus. 14C-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 14C-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.

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