We have isolated lentivirus strains that are related to the human immunodeficlency virus (HIV) from African green monkeys (Cercopithecus aethiops; AGM). Although immunologically related, these SIVMM are clearly distinct from other simian immunodeficiency virus (SIV) isolates, including isolates from Macaca mulatto (SaIV ) or even from other AGM. The SIVNK strains described in this communication grow well in a limited number of human T-lymphoma lines. Virus density, morphology, and reverse transcriptase activity are characteristic of the lentivirus group.

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Simian immunodeficiency viruses have been isolated from African green monkeys originating from Ethiopia. A molecular clone, termed SIVagm3, was found to be highly divergent from SIVagmTYO-l in terms of its restriction map and partial nucleotide sequence. A premature stop codon present in the transmembrane protein of SIVagm TYO-l was absent in SIVagm3. SIVagm3 was biologically active in vitro and in vivo and displayed characteristics reminiscent of the wild-type virus. Biological activity was demonstrated by seroconversion of juvenile African green monkeys and Macaca nemestrina after inoculation. In contrast to antibody reactivity mainly directed against env proteins in naturally infected African green monkeys. African green monkeys and M. nemestrina infected with the cloned virus showed antibody reactivity directed against all major proteins as demonstrated by immunoblot analysis. The availability of a biologically fully competent molecular clone of SIVagm allows us now to address various pertinent questions in an animal model system which should help to understand features of human immunodeficiency virus infection in human beings.

Isolation of early viral transcriptional complexes and incorporation in vitro of radiolabeled precursors into nascent RNA has permitted an analysis of early simian virus 40 (SV40) transcription. Under conditions such that viral DNA replication was undetectable, both early and late SV40 RNA were synthesized. This finding provides evidence that viral DNA replication is not an absolute requirement for late transcription and supports earlier observations that late viral RNA is synthesized in SV40-infected nonpermissive mouse cells. The majority of the early viral transcriptional activity can be solubilized, indicating that a substantial portion of this RNA is transcribed from free rather than integrated templates. Sedimentation analysis of the transcriptional complexes resulted in the detection of two separate peaks of activity, suggesting the possibility of two distinct types of early SV40 templates.It has been known for some time that simian virus 40 (SV40) RNA is synthesized in two phases (1-3). Prior to viral DNA replication, most of the viral mRNA appears to be transcribed from the early DNA strand (4-6). Subsequently, the bulk of viral transcription occurs from the late DNA strand and is processed into late 16S and 19S viral mRNAs (7,8). It was generally assumed that this late phase of viral transcription was inextricably linked to viral DNA replication (see refs. 9 and 10). The absence of the late SV40 transcripts in most SV40-transformed cell lines supported this concept (11). Nevertheless, we consistently found late viral RNA sequences in abortively infected mouse cells, in which SV40 DNA replication could not be detected (5, 12). Furthermore, recent studies with early temperature-sensitive mutants of SV40 grown at 410 (the nonpermissive temperature) indicated the presence of a small but reproducible fraction of late virus-specific cytoplasmic RNA (13). This led us to speculate that viral DNA replication was not an absolute requirement for the transcription of sequences on the late SV40 DNA strand. It was difficult to test this hypothesis directly, because of the low levels of late virus-specific RNA found prior to viral DNA replication (1-6, 14) and the potential rapidity and efficiency of the RNA processing system (15).We recently described the adaptation of an in vitro transcriptional system (16) established by Gariglio and Mousset (17). The supernatant fraction of SV40-infected cell nuclei, lysed in the presence of Sarkosyl, actively incorporates radiolabeled ribonucleotide triphosphates, and the newly synthesized RNA can be easily analyzed. Although it is unclear whether putative termination signals are recognized under such incorporation conditions, the absence of reinitiation allows one to assess accurately the frequency of in vivo transcription of the two viral DNA strands (16). Further advantages of this in vitro transcriptional system include: (i) the enrichment of virus-specific RNA sequences in the nuclear supernatant fraction; (ii) an increase in the specific activity of the viral RNA t...