CHARACTERIZATION OF A PSEUDORABIES VIRUS THAT IS DEFECTIVE IN THE EARLY PROTEIN-0 AND LATENCY GENES

A recombinant pseudorabies virus that is defective in the early protei n 0 (EP0) and large latency transcript (LLT) genes was constructed. A portion of the EP0 and LLT genes was replaced by the lacZ gene of Esch erichia coli that had been placed under the control of the pseudorabie s virus gX gene promoter. This recombinant virus produces smaller size plaques and yields less virus than does the parent virus on Madin-Dar by bovine kidney cells. Although the time course of virus replication and release into the medium of the recombinant and parent viruses are similar, the recombinant virus did not reach as high a titer. Similar to the parent virus, the recombinant virus replicates in the upper seg ment of the respiratory tract of swine, but the amount of progeny viru ses produced is significantly reduced. The data indicated that the EP0 and LLT genes of pseudorabies virus are nonessential for replication. Virus that lacks these 2 genes has impaired growth in tissue culture and is attenuated for swine, compared with the parent virus.