On the stability of sequences inserted into viral genomes

Willemsen, Anouk; Zwart, Mark P

When considering the size of the insert and its stability, ssRNA(À) viruses accept relatively large insert without drastically affecting virus replication. Sendai virus, with a genome size of about 15.3 kbp, can carry and efficiently express gene insertions up to 3.2 kbp (Sakai et al. 1999) . However, also here the insert size is limited, where the final virus titers in vitro are proportionally reduced as the insert size increases. While in vivo no such size-dependent effect was observed, an attenuated replication and pathogenicity were detected (Sakai et al. 1999) . Insertions up to 3.9 kbp in the $15.4 kbp genome of the human parainfluenza virus 3 were viable and replicated efficiently in vitro (Skiadopoulos et al. 2000) . Nonetheless, the insertions longer than 3,000 bp reduced the robustness to environmental perturbation of the virus, as temperature sensitivity was augmented and replication was restricted to certain sites in vivo (Skiadopoulos et al. 2000) .