Characteristics of the adeno-associated virus preintegration site in humanchromosome 19: Open chromatin conformation and transcription-competent environment

Adeno-associated virus (AAV) establishes latency in infected cells by integ rating into the cellular genome, with a high preference for a unique region , called AAVS1, of the human chromosome 19. The AAV proteins Rep78 and -68 are postulated to initiate the site-specific integration process by binding to a Rep binding site (RBS) in AAVS1. We provide further evidence to corro borate this model by demonstrating that the AAVS1 RES in human cell lines i s located near a DNase I hypersensitive ''open" chromatin region and theref ore is potentially easily accessible to Rep proteins. This open conformatio n is maintained in transgenic rats which carry an AAVS1 3.5-kb DNA fragment and are proficient for Rep-mediated site-specific integration. Interesting ly, the core of the DNAse I hypersensitive site in AAVS1 corresponds to a s equence displaying transcriptional enhancer-like properties, suggesting tha t AAVS1 constitutes a transcription-competent environment. The implications of our findings for AAV physiology and gene therapy are discussed.