CELLULAR-COMPONENTS INTERACT WITH ADENOVIRUS TYPE-5 MINIMAL DNA PACKAGING DOMAINS

Adenovirus type 5 DNA packaging is initiated from the left end of the viral genome and depends on the presence of a cis-acting packaging dom ain located between nucleotides 194 and 380. Multiple redundant packag ing elements (termed A repeats I through VII [AI through AVII]) are co ntained within this domain and display differential abilities to suppo rt DNA packaging in vivo. The functionally most important repeats, AT, AII, AV, and AVI, follow a bipartite consensus motif exhibiting AT-ri ch and CG-rich core sequences. Results from previous mutational analys es defined a fragment containing AV, AVI, and AVII as a minimal packag ing domain in vivo, which supports a functional independence of the re spective cis-acting sequences. Here we describe multimeric versions of individual packaging elements as minimal packaging domains that can c onfer viability and packaging activity to viruses carrying gross trunc ations within their left end. These mutant viruses directly rate the f unctional role that different packaging elements play relative to each other. The A repeats are likely to be binding sites for limiting, tra ns-acting packaging factors of cellular and/or viral origin. We report here the characterization of two cellular binding activities interact ing with all of the minimal packaging domains in vitro, an unknown bin ding activity termed P-complex, and the transcription factor chicken o valbumin upstream promoter transcription factor. The binding of both a ctivities is dependent on the integrity of the AT-rich, but not the CG -rich, consensus half site. In the case of P-complex, binding affinity for different minimal packaging domains in vitro correlates well with their abilities to support DNA packaging in vivo. Interestingly, P-co mplex interacts not only with packaging elements but also with the lef t terminus of the viral genome, the core origin of replication. Our da ta implicate cellular factors as components of the viral packaging mac hinery. The dual binding specificity of P-complex for packaging and re plication sequences may further suggest a direct involvement of left-e nd replication sequences in viral DNA encapsidation.