No abstract

Apoptosis in HIV-1-infected CD4+ primary T cells is triggered by the alteration of the PI3K and p53 pathways, which converge on the FOXO3a transcriptional activator. Tat alone can cause activation of FOXO3a and of its proapoptotic target genes. To understand how Tat affects this pathway, we carried out ChIP-Chip experiments with Tat. Tat associates with the promoters of PTEN and two PP2A subunit genes, but not with the FOXO3a promoter. PTEN and PP2A encode phosphatases, whose levels and activity are increased when Tat is expressed. They counteract phosphorylation of Akt1 and FOXO3a, and so activate transcriptional activity of FOXO3a. FOXO3a promotes increased transcription of Egr-1, which can further stimulate the transcription of PTEN, thereby reinforcing the pathway that leads to FOXO3a transcriptional activation. RNAi experiments support the role of PTEN and PP2A in the initiation of the Tat-mediated cascade, which is critical to apoptosis. The increased accumulation of PTEN and PP2A subunit mRNAs during Tat expression is more likely to be the result of increased transcription initiation and not relief of promoter-proximal pausing of RNAPII. The Tat-PTEN and -PP2A promoter interactions provide a mechanistic explanation of Tat-mediated apoptosis in CD4+ T cells.

L protein of hantaviruses is the RNA transcriptase and replicase that transcribes mRNAs and replicates the genomic RNA using antigenomic RNA as an intermediate. It also appears to have endonuclease activity. In this review, the current knowledge on the hantavirus L protein is presented including sequence motifs conserved in RNA polymerases, mechanisms of RNA synthesis and also the most recent findings on homologous RNA recombination and membrane association.

Since the discovery of RNA recombination in polioviruses, there has been a general belief that this mechanism operates only in positive-sense RNA viruses. Recently, studying wild-type Tula hantavirus, we observed a mosaic-like structure of the S RNA segment that was consistent with generation by recombination between viruses from two genetic lineages. Here we show transfection-mediated rescue of Tula virus carrying recombinant S RNA segment. Independent attempts yielded S RNA molecules of similar structure; the majority of them carried a break point located close to one of the break points suggested for natural recombinants. Recombinant virus puri®ed from the original variant was able to grow to the same titers in cell culture and showed the same characteristic immuno¯uorescence pattern when stained for the nucleocapsid protein. While competent, the recombinant virus appeared to be slightly less competitive than the wild type. Sequence analysis of the S cDNA clones obtained from the puri®ed recombinant virus con®rmed that all S RNA molecules were of recombinant origin. This provides the ®rst example of a negative-sense RNA virus constructed using homologous recombination.