Abstract: The present invention provides an expression vector adapted for inducible amplification and inducible transcription of a heterologous polynucleotide operably linked to a transcriptional promoter provided in the vector. The invention further provides a method for using the vector to produce large quantities of a heterologous polypeptide encoded by the heterologous polynucleotide. The pBAC of the present invention is derived from a BAC cloning vector by modifying the BAC cloning vector to include a conditional ori for amplifying the pBAC and an inducible promoter for regulating the transcription of an inserted gene. Both the conditional ori and the inducible promoter can be activated jointly or separately by suitable signals in a host cell.

Abstract: The present invention provides an expression vector adapted for inducible amplification and inducible transcription of a heterologous polynucleotide operably linked to a transcriptional promoter provided in the vector. The invention further provides a method for using the vector to produce large quantities of a heterologous polypeptide encoded by the heterologous polynucleotide. The pBAC of the present invention is derived from a BAC cloning vector by modifying the BAC cloning vector to include a conditional ori for amplifying the pBAC and an inducible promoter for regulating the transcription of an inserted gene. Both the conditional ori and the inducible promoter can be activated jointly or separately by suitable signals in a host cell.

Abstract: Construction of a recombinant bacterial host which is substantially immune to a normally infectious viral agent is disclosed. In one embodiment a foreign recombinant reproducible gene segment is inserted into the bacterial cell. The gene segment is a partially defective variant of a gene segment from the infectious virus of interest. The viral gene segment, in its naturally occurring and fully operational form, normally codes for a non-repressor protein which participates in a multi-protein complex used in the development of the virus. However, the partially defective gene present in the bacterial cell codes for a defective protein that will bind to the remainder of the multi-protein complex with a greater affinity than the virus' fully operational protein. The "new" protein complex will therefore be inactive and will inhibit the ability of the foreign agent to use the multi-protein complex for its development.