CHARACTERIZATION OF A HERPES-SIMPLEX VIRUS TYPE-1 DELETION VARIANT (1703) WHICH UNDER-PRODUCES VMW63 DURING IMMEDIATE-EARLY CONDITIONS OF INFECTION

The herpes simplex virus type 1 deletion variant 1703 apparently fails to synthesize the essential IE2 gene product Vmw63 despite the deleti on leaving the gene intact. Sequence analysis revealed that the deleti on removes a region to the right of IE2 comprising the 3' end of IE1, UL56 and the 3' part of UL55, stopping 555 bp downstream of the IE2 po lyadenylation signal. Further DNA sequencing has shown that there is n o secondary mutation in the IE2 gene. Western blot analysis demonstrat ed that Vmw63 is made at reduced levels compared to that produced by t he wild-type virus during immediate early conditions of infection. S1 nuclease protection mapping has revealed that this reduction is also a pparent at the level of mRNA synthesis. A direct link between the dele tion and the change in mRNA synthesis was provided by the insertion of a deletion-spanning fragment from 1703 into a 17(+) genome, which res ulted in the recombinant having a 1703-1ike phenotype. Evidence that d own-regulation of IE2 mRNA during immediate early conditions of infect ion could be due to antisense RNA initiating from the IE1 promoter was obtained by the insertion of a novel transcriptional termination sign al between IE1 and IE2 in the variant and the subsequent detection of wild-type levels of IE2 mRNA and protein.