Explanation: The dependence of AAV on a heterologous helper virus provides an unusual degree of control over vector replication, making AAV one of the safest vectors for use in gene therapy.

Explanation: In vitro manipulation of AAV is facilitated by cloning the inverted terminal repeats in a plasmid vector and inserting the transgene between them.

Explanation: Few experiments were conducted in which both cap and rep genes were deleted and transgene was expressed from either a heterologous or endogenous promoter. It was then demonstrated that the repeats are only elements required for replication.

Explanation: Few experiments were conducted in which both cap and rep genes were deleted and transgene was expressed from either a heterologous or endogenous promoter.

Explanation: Deletion of the rep region abolishes the site specificity of proviral integration, so the vector integrates at essentially random positions.

Explanation: AAV vectors have been used to introduce genes efficiently to many cell types, including liver, muscle and neurons.

Explanation: The fact that AAV uses con-catemeric replication intermediates has been used to circumvent perhaps the most serious disadvantage of AAV vectors, which is limited capacity for foreign DNA.

Explanation: One group of baculoviruses, known as the nuclear polyhedrosis viruses, has an unusual infection cycle that involves the production of nuclear occlusion bodies.

Explanation: Nuclear occlusion bodies are proteinaceous particles in which the virions are embedded, allowing the virus to survive harsh environmental conditions such as desiccation.

Explanation: The occlusion bodies are relevant to vector development because they consist predominantly of a single protein called polyhedron at very high levels.

Explanation: The nuclear occlusion stage of the infection cycle is non-essential for the productive infection of cell lines, thus the polyhedrin gene can be replaced.

Explanation: Autographa californica multiple nuclear polyhedrosis virus (AcMNPV) is used for protein expression in insect cell lines, particularly those derived from Spodoptera frugiperda.

Explanation: BmNPV infects the silkworm and has been used for the production of recombinant protein in live silkworm larvae.

Explanation: One limitation of the expression system is that the glycosylation pathway in insects differs from that in mammals, so recombinant mammalian proteins may be incorrectly glycosylated and hence immunogenic.

Explanation: The issue of incorrectly expressed mammalian recombinant proteins is addressed by using insect cell-lines chosen specifically for their ability to carry out mammalian-type post-translational modifications.