A mutant herpesvirus has inactivating (preferably deletion) mutations at the locus of both native copies of the latency-active regulatory sequences. The resulting virus can be used as a latency-inactive virus as the basis of vectors for gene delivery, as a helpervirus for production of amplicons, and as a base virus mutant for the construction of mutant virus vectors carrying synthetic latency-active regulatory sequences. Also described are synthetic/semisynthetic latency-active regulatory sequences and their use in CNS and other cells.
Virus vectors and expression elements