Biomedical subjects

U Fleps

Publications and source records attributed to U Fleps.

4 recordsLinked to original sources

PubMed1996

Transactivation of the two promoters of SFV-3 by different mechanisms.

Simian foamy virus type 3 (SFV-3), a member of the spumavirus genus of retroviruses, has a complex genome organization and encodes two open reading frames (ORFs), in addition to the structural genes gag, pol, and env. ORF-1 encodes a viral transcriptional transactivator designated Taf (transactivator of foamy viruses) which augments transcription from the viral long terminal repeat (LTR). It was recently shown that human foamy virus, as well as the simian viruses SFV-1 and SFV-3, contains a second internal transcriptional promoter in the transmembrane domain of the env gene; this promoter also is transactivated by Taf. Here we report the characterization of the internal promoter of SFV-3. The transcriptional start site of this promoter has been mapped in two different SFV-3-infected cell lines to nt position 9761 in the proviral genome of SFV-3. All cis-regulatory elements required for transactivation by Taf are located between -202 and -32 (+1 representing the transcription initiation site in the internal promoter). Analysis of hybrid promoter constructs and deletion mutants in transient expression assays revealed that this region contains two elements which are independently responsive to Taf. In addition, we employed an in vivo DNA competition assay to determine whether the transactivation mechanisms of both SFV-3 promoters are similar or different. The differences observed utilizing this competition assay suggest that Taf transactivates the internal promoter and the LTR through different cellular transcription factors.

Animals↗

PubMed1993

Simian foamy virus type 3 (SFV-3) in latently infected Vero cells: reactivation by demethylation of proviral DNA.

Cell cultures latently infected with simian foamy virus type 3 (SFV-3) were established by suppressing lytic infection in Vero cells with 3'-azido-3'-deoxythymidine (AZT) and homologous antibodies (African green monkey serum immune to SFV-3). The resulting cell line, designated Vero-L, was shown to contain at least one copy per cell of SFV-3 DNA stably integrated at a defined site of the host cell genome. Sequencing of 669 bp at the integration site did not identify a coding region and revealed a 4-bp imperfect repeat in host cell DNA due to SFV-3 integration. Over 2 years of subcultivation, no spontaneous expression of proviral genes could be detected. However, the demethylating agent 5'-azacytidine reactivated lytic infection, proving conservation of the complete viral genome. Comparison of proviral DNA from latently and lytically infected cells supports the notion that methylation is instrumental in keeping SFV-3 infection in latency.

Animals↗

PubMed1993

Foamy viruses.

Foamy viruses share complex genome organization with lentiviruses and certain oncoviruses. The open reading frame 3' of env encodes a transcriptional transactivator. Distinct responsive sequences were identified in the long terminal repeats (LTRs) of simian (SFV-1 and SFV-3) and human foamy viruses (HFV). Transactivation of heterologous LTRs was described including those of simian and human immunodeficiency viruses. Foamy viruses persist for the whole lifetime in infected hosts (primates, cats, hamsters, cattle, and probably other mammals). The virus may be orally shed and transmitted, while being latent in various internal organs. Selective viral gene expression in the brains of mice transgenic for HFV has suggested a particular relationship to neural tissue. In latently SFV-3-infected cultured cells, methylation of proviral DNA is apparently involved in the control of latency. Demethylation as well as transfection with the transactivator were shown to be instrumental in viral reactivation. Natural infections with foamy viruses are common, elicit strong immune responses, and seem to be asymptomatic in nonhuman primates. Detection of such infections, however, may not be a triviality in man. While accidental transmission of foamy viruses to man is well documented, reported seroprevalence in human populations and the association of HFV with specific pathology (e.g. thyroiditis de Quervain, amyotrophic lateral sclerosis, and Graves' disease) are controversial and remain to be proven.

Animals↗

PubMed1992

Genomic organization and expression of simian foamy virus type 3 (SFV-3).

The complete nucleotide sequence of simian foamy virus type 3 (SFV-3) strain LK-3, isolated from an African green monkey, was determined. In addition to translation frames representing the gag, pol, and env genes, two open reading frames are located in the region between the env gene and the 3' long terminal repeat (LTR). Both SFV-3 and SFV-1 encode two open reading frames between env and the 3' LTR, whereas HFV encodes three open reading frames in this region. Northern blot analysis of cell cultures infected with SFV-3 revealed subgenomic RNAs for these open reading frames. The protease of SFV-3 is encoded by the pol gene in contrast to HFV which encodes the protease in the gag gene. Notably, the pol gene of SFV-3 in the +1 translational frame relative to the gag gene; this observation is in agreement with SFV-1, but differs for HFV and all other retrovirus genomes reported. Thus, gag-pol precursors of the SFVs appear to be expressed by a +1 frameshift. Nucleotide and deduced amino acid alignments of SFV-3, SFV-1, and HFV revealed an unexpected homology pattern; highest homologies are observed in the pol and env genes but low homologies are noted in the gag genes and the additional open reading frames. Analysis of phylogenetic trees confirms the classification of foamy viruses as a subfamily of retroviruses, distinct from the lentiviruses and oncoviruses.

Amino Acid Sequence↗