These vectors contain a transcriptional regulatory sequence (which may be any transcriptional regulatory sequence, including but not limited to the promoters, enhancers, and repressors described herein, and which preferably is a promoter or an enhancer, and most preferably a promoter such. as a CMV immediate early gene promoter, an SV40 T antigen promoter, a tetracycline-inducible promoter, or a ?