In the present invention, viruses, plasmids or both are constructed which
contain viral DNA and lox sites positioned such that site-specific
recombination between lox sites in separate plasmids results in
generation of infectious viral DNA at high-efficiency in cotransfected
host cells that have been engineered to express the Cre recombinase.
Because of the high-efficiency and specificity of the Cre enzyme,
suitably engineered plasmids can be readily recombined to produce
infectious virus at high-efficiency in cotransfected 293 cells, without,
at the same time, producing wild-type adenovirus, with the attendant
problems for removal thereof. Use of recombinases besides Cre and
recombinase recognition sites besides lox sites, and use of cells other
than 293 cells are also disclosed and enabled, as are kits incorporating
the site-specific vector system.