The adenovirus genome is a linear, 36-Kb double-stranded DNA (dsDNA) molecule containing multiple, heavily spliced transcripts. At either end of the genome are inverted terminal repeats (ITRs). Genes are divided into early (E1-4) and late (L1-5) transcripts. There are 57 accepted human adenovirus types, and most adenoviral vectors are based on Ad5. Ad5-based vectors use the Coxsackie-Adenovirus Receptor (CAR) to enter cells. Recombinant adenovirus has two genes deleted: E1 and E3. E1 is supplied by the adenovirus packaging lines 293 or 911; its deletion from the viral vector renders the virus replication incompetent. E3 is involved in evading host immunity and is not essential for virus production. Deletion of these two components results in a transgene packaging capacity of >8 Kb. Constructs contain left and right arms to facilitate homologous recombination of the transgene into the adenoviral plasmid.
Overview of Adenoviral Plasmid System