Abstract: The invention provides a two component system for in vitro cloning of a heterologous polynucleotide into adenoviral DNA. The first component is an insert donor comprising a heterologous polynucleotide encoding a heterologous polypeptide. The second component is a vector donor comprising an adenovirus genome and an expression cassette. The insert donor and vector donor are adapted for site specific recombination using recombination sites from phage lambda for insertion of the heterologous polynucleotide into the expression cassette capable of forming an adenoviral expression clone in vitro in the presence of a suitable recombination mediator protein or proteins. The invention also provides a method of making recombinant adenovirus and use of the first and second components in such a method.

Abstract: An improved T7 based promoter-driven protein expression system comprising an operator sequence downstream of the T7 promoter sequence, and having a further operator sequence upstream of the T7 promoter sequence.