IDENTIFICATION OF A REGION OF THE ALCELAPHINE HERPESVIRUS-1 GENOME ASSOCIATED WITH VIRULENCE FOR RABBITS

The gammaherpesvirus Alcelaphine Herpesvirus 1 (AHV-1) causes the fata l lymphoproliferative disease known as malignant catarrhal fever (MCF) , in susceptible hosts. The virulent C500 isolate of AHV-1 became atte nuated for the laboratory model, the rabbit, as a result of serial pas sage in cells of bovine origin. This work describes the identification of a region of the central unique sequence of the C500 genome, locate d close to the terminal repeat units of the molecule, which is altered on attenuation. The virulent C500 genome contains two copies of a seq uence of approximately 2 kbp, contained within a 7 kbp region of the u nique DNA located adjacent to the terminal repeats at the left end of the molecule. In the genome of the attenuated virus, there are also tw o copies of the 2 kbp sequence but they are located at the ends of the attenuated genome unique region, adjacent to the terminally repeated sequences. One open reading frame (ORF), designated putative polypepti de 5, was altered on attentuation such that the 3' sequence was lost. The location of this ORF, coupled with the loss of its 3' sequence, su ggests that this ORF may encode a gene involved in the virulent mechan isms of this virus, in a manner similar to that of the transforming pr oteins of Herpesvirus saimiri (HSV).