Visna virus DNA: Discovery of a novel gapped structure

FIV: from lentivirus to lentivector

“…Visna and HIV-1, and human/simian spumaviruses as well, contain an exact copy of their respective PPTs in pol [110,111]. In the pre-integration complexes of these viruses, a plusstrand gap corresponding to a second site of plus-strand initiation has been detected at this central PPT (cPPT) [105,106,[112][113][114][115][116][117]. The net outcome is that the plus strand of the PIC contains two discrete half-genomic DNA segments.…”

“…The pre-integration complex (PIC) has a mass of several million Daltons and a Stokes radius of 20-30 nm (it is roughly equivalent to or greater in size than a eukaryotic ribosome), so it is clear that, in directing import of this structure though the nuclear pore (Figure 1), lentiviruses have evolved to surmount a substantial problem (reviewed in [101][102][103]). For HIV-1, considerable evidence has been put forward for nuclear import determinants in virion proteins [98,99], and, more recently, for a role for a central plus-strand discontinuity, or flap [104], found in the PIC [61,105,106]. Retroviral (−)strand synthesis generates a (+)RNA/ (−)DNA duplex [107].…”

Reverse Transcriptase Jumps and Gaps

“…In contrast, lenti-and spumaviruses establish productive infections with a high quantity of linear unintegrated DNA (lyric-like cycle). However, for MW and the spumaviruses, the integrated proviral state is, if it ever exists, very difficult to detect (Harris et al, 1981;Kupiec et al, 1988). Recently, it has been shown that spumaviruses encapsidate DNA molecules and replicate through an unusual pathway reminiscent of hepadnaviruses (Yu et al, 1996).…”

Biology and Pathogenesis of Lentiviruses

“…In contrast only a small proportion of lentiviral DNA becomes circularized and only a small number of copies become integrated in each infected cell CYaniv et al, 1985;Chiu et al, 1985). However, many more copies (100 to 200) per cell are found as free linear dsDNA molecules in the nucleus of the infected cell (Clements et al, 1979;Harris et al, 1981). In other retroviral systems, the integrated viral DNA is the most efficient template for viral RNA transcription (Panganiban & Temin, 1983).…”

“…The lentiviral genome, larger than that of oncogenic retroviruses, is a positive-stranded polyadenylated RNA of 9000 to 10000 bp (Clements & Narayan, 1981;Harris et al, 1981 Ratner et al, 1985;Sonigo et al, 1985). The rectangles delineate ORFs (except for the 5' and 3' LTRs), showing the proteins that are encoded.…”