Visna virus is a nontransforming retrovirus that causes slow infections in animals and a rapidly progressive-lytic infection in cell culture. The results of an analysis of the synthesis of viral DNA in cell culture are reported. Region- and strand-specific probes cloned in M13 have been used to define the dynamics of DNA synthesis and the major nucleic acid species formed. It is shown that (i) within the first hours of infection, a full-length copy of the viral RNA genome is synthesized by reverse transcription, (ii) early in infection a major species of DNA is formed that extends from a site near the center of the molecule to the 3′ end, (iii) somewhat later a second major species of plus-strand DNA is generated that extends from the 5′ end to the middle of the genome. As a consequence, most viral DNA molecules consist of a full-length minus strand, and two plus strands separated by a gap or nick in the center of the molecule (J. D. Harris, J. V. Scott, B. Traynor, M. Brahic, L. Stowring, P. Ventura, A. T. Haase, and R. Peluso (1981). Virology, 113, 573-583). The implications of this viral DNA structure for one unusual aspect of the lentivirus life cycle, the production of viral RNA, and virions from extrachromosomal DNA are discussed (J. D. Harris, H. Blum, J. Scott, B. Traynor, P. Ventura, and A. T. Haase (1984). Proc. Natl. Acad. Sci. USA, 81, 7212-7215).
Bibliographical noteFunding Information:
Much of this work was completed at the VAMC in San Francisco and was supported by basic institutional mechanisms of the Veterans Administration. We also acknowledge grant support from the NIH, National Multiple Schlerosis Society, and American Cancer Society. We thank Linda Livermore and Jan Torma for preparation of the manuscript. Ashley T. Haase was a Medical Investigator of the Veterans Administration in the course of this work. Hubert E. Blum is a Heisenberg fellow of the Deutsche Fo~hungsgemeins~haft.
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