The Roles of AAV Rep Proteins in Gene Expression and Targeted Integration

Adeno-associated virus 2 (AAV), a nonpathogenic human virus, can either integrate into host chromatin and remain latent or replicate following infection. The outcome depends on the cellular conditions. Under conditions permissive for AAV DNA replication (e.g., during adenovirus coinfection), AAV gene expression is induced. The single-stranded AAV genome of 4680 nucleotides is organized into two open reading frames (ORFs) that encode structural capsid proteins (Cap) and nonstructural proteins (Rep) (Fig. 1). Two promoters at AAV map units 5 and 19, p5 and p19, direct expression of the rep gene. The cap gene is regulated by the p40 promoter. A common intron results in the production of four Rep proteins: p5 initiated Rep78, Rep68 and p19 initiated Rep52, Rep40. The inverted terminal repeats (ITRs) function as viral origins of replication required for encapsidation of the of AAV DNA. The production of AAV Rep proteins enables viral DNA to replicate, resulting in a geometric increase in the number of viral genomes. The AAV p5 initiated regulatory proteins Rep78 and Rep68 interact with the viral promoters to establish a feedback loop. These Rep proteins are involved directly in viral DNA replication as well.