Visna virus is the prototypic member of a subfamily of retroviruses responsible for slow infections of animals and humans. As a part of our investigation of the functions of viral gene products in virus replication, we have isolated three infectious molecular clones and determined the complete nucleotide sequences of two of the clones. We have also characterized the progeny of the biologically cloned viral stocks and of the infectious clones and document considerable heterogeneity in plaque size and antigenic phenotype of the former that is reduced to near homogeneity in the progeny of the infectious clones. It thus should now be possible to trace the emergence of antigenic variants of visna virus as well as ascribe defined functions to structural and regulatory genes of the virus in determining neurovirulence and the slow tempo of infection.
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We thank Robert Storms and Dennis Anderson for helpful discussions regarding E. co/i hosts and computational analysis, respectively, and the University of Minnesota Department of Microbiology Teaching Lab for technical support during part of the sequencing phase of the project. We also thank Tim Leonard for help in preparation of the figures. This work was supported by a grant from the National Institutes of Health (NS2 1423).