Visna virus RNA synthesis

Visna is a classical slow infection in which virus characteristically persists in the face of the host immune response. The agent of this disease belongs to the retravirus group. The persistence of infection and the slow spread of virus are at least in part a consequence of restriction of the expression of virus genetic information in tissues of an infected animal, but the point at which the virus life cycle is interrupted in vivo and the mechanism of restriction are unknown, a reason for a study on the molecular analysis of restriction, focusing first on transcription. In this paper the levels of viral RNA synthesis under permissive conditions are established, as a base line for subsequent studies in vivo. It is shown that uninfected cells do not contain RNA sequences related to the visna virus genome, that parental RNA is rapidly transported to the nucleus of the infected cell, that virus RNA is synthesized in the nucleus and then transported to the cytoplasm, that synthesis of RNA proceeds mostly exponentially to reach levels of about 4,000 copies per cell at the end of the growth cycle, that nuclear and cytoplasmic RNA sediment in 2 size classes, 35S and 10-20S, that viral mRNA has the same polarity as genome RNA and also sediments in 2 size classes of 35S and 10-20S.