1. Cultures of chick-embryo fibroblasts were exposed to chicken plasma containing avian myeloblastosis virus and the incorporation of [2-14C]uridine into virussized particles of the culture supernatant was studied. 2. These particles, when examined by sedimentation in sucrose gradients and by electron microscopy, resembled virus particles from leukemic plasma. No particles were evident in control cultures. 3. Particles formed by virus-exposed chick-embryo fibroblasts sedimented somewhat more rapidly in sucrose gradients than those formed by myeloblasts. 4. The incorporation of [2-14C]uridine into these particles by chick-embryo fibroblasts was inhibited by a low concentration of actinomycin D. 5. There was no detectable additional RNA synthesis resistant to actinomycin D in virus-exposed fibroblasts compared to control fibroblasts.
Bibliographical noteFunding Information:
Support was providedb y grants from the American Cancer Society (E-277 and E-278B) and U.S. Atomic Energy CommissionC ontractNo. AT(30-I)-2643. I am indebtedt o Dr. P. C. ZAMECNIK for advice and encouragementto, Drs. B. R. BURMESTER and H. G. PURCHASE for supplieso f virus, to Dr. J. W. LITTLEFIELD for his help with tissue-culturtee chniquesa, nd to Miss LYNN R. C0ZZA for expert assistance. This is publicationN o. 1241 of the CancerCommissionof Harvard University.