On the stability of sequences inserted into viral genomes

Willemsen, Anouk; Zwart, Mark P

Retro-transcribing ssRNA(þ) viruses, or retroviruses, are small viruses varying in genome size from 7 to 11 kbp and are classified in the Retroviridae family. After entering a host cell, the retroviral RNA genome is converted into dsDNA by reverse transcription. The viral DNA integrates into the host genome, where viral genes are translated. Therefore, these viruses are often used for gene therapy. Retroviruses frequently undergo genomic rearrangements, including gene insertions and deletions (indels). Moreover, recombination can be common due to the combination of 'diploid' virus particles and high intrinsic recombination rates (Jetzt et al. 2000) . Therefore as a general observation this viral group appears to have a highly plastic genome, and should be relatively open to foreign gene insertions. As retroviruses integrate into the host genome, the stability of inserts does not necessarily depend solely on the retrovirus genome configuration and demographic conditions. As host genomes are in general less streamlined than those of viruses, one could expect that gene insertions are stable after integration into the host genome. However, the random integration of retroviruses in the host genome makes it hard to predict genomic stability.