Explanation: The large genome and structural complexity of the virus is because it must encode and package all its own DNA replication and transcription machinery.

Explanation: Since the virus normally packages its own replication and transcription enzymes, recombinant genomes introduced into cells by transfection are generally non-infectious.

Explanation: In one selection regime strategy, the transgene is inserted into the viral TK gene and negative selection using the thymidine analog 5-bromodeoxyuridine.

Explanation: When transgene is inserted into the viral hemagglutinin locus, if chicken erythrocytes are added to the plate of infected cells, wild-type plaques turn red and recombinants turn clear.

Explanation: Since vaccinia vectors have a high capacity for foreign DNA, selectable markers such as NEO can be co-introduced with the experimental transgene to identify recombinants.

Explanation: Since vaccinia vectors have a high capacity for foreign DNA, screenable markers such as LacZ’ can be co-introduced with the experimental transgene to identify recombinants.

Explanation: Transgene expression usually needs to be driven by an endogenous vaccinia promoter, since transcription relies on proteins supplied by the virus.

Explanation: The highest expression levels are provided by late promoters such as P11, allowing the production of up to 1 microgram of protein.

Explanation: Since the cytoplasm lacks not only host transcription factors but also the nuclear splicing apparatus, vaccinia vectors cannot be used to express genes with introns.

Explanation: The sequence TTTTTNT must be removed from all foreign DNA sequences expressed in Vaccinia vectors since the virus uses this as a transcriptional terminator.

Explanation: A useful binary expression system has been developed, in which the transgene is driven by the bacteriophage T7 promoter and the T7 polymerase.

Explanation: The vaccinia virus cannot be used to express antigens from other infectious agents by replacing the Vaccinia Tk locus with transgene encoding hepatitis B surface antigen.

Explanation: The transgene is cloned in a plasmid and this plasmid is then transfected into vaccinia-infected monkey cells, and recombinant vectors are then selected.

Explanation: Vaccinia viruses expressing the influenza hemagglutinin gene are used to immunize hamsters, and induce resistance to influenza.

Explanation: Monkeys infected with recombinant vaccinia and canarypox vectors have shown resistance SIV and HIV-2.