Spontaneous mobilization of integrated recombinant adenoassociated virus in a cell culture model of virus latency.

A cell line containing integrated recombinant adenoassociated virus (AAV) was investigated for spontaneous mobilization of vector sequence. Detection of these rare events was facilitated by using a vector design that allowed the circular rescue product (cAAV) to be individually scored by bacterial transformation. Restriction and sequence analysis of captured clones revealed five highly ordered classes of cAAV, each of which contained a defined segment of the integrated vector locus. A common feature of all cAAV classes was the presence of a modified inverted terminal repeat that joined the ends of the liberated sequence. Assembly of extrachromosomal vector genomes was accompanied by deletions in the integration locus that could be mapped to one of the five cAAV classes, suggesting an excision-type mechanism. We propose that the spontaneous deletion and mobilization of vector sequence from the recombinant adenoassociated virus (rAAV) integration locus is mediated by a recombination event between the inverted terminal repeats that define the boundaries of the individual genome subunits.