The spontaneous reactivation function of the herpes simplex virus type 1 LAT gene resides within the first 1.5 KB of the 8.3 KB primary transcript

Purpose. To map the region of LAT involved in enhancing spontaneous reactivation. Methods. To make the mutant LAT15a, the LAT promoter and the first 1.5 kb of the 8.3 kb LAT gene were inserted into the unique long region of an HSV-1 (strain McKrae) mutant lacking the LAT promoter and the first 1.67 kb of both copies of the LAT gene (one in each long repeat). Rabbits were ocularly infected and spontaneous reactivation measured. Results. 55 of 468 (12%) tear films from rabbits latently infected with LAT15a contained spontaneously reactivated virus. This was significantly higher than the LAT negative mutant (0%; 0/312; p<0.0001, Fisher exact test) and not different from marker rescued virus (70/624; 11%; p=0.85). Southern analysis confirmed that the reactivated LAT15a virus retained the original deletions in both copies of LAT and the 1.5 kb LAT insertion in the unique long region. Conclusions. Insertion of the first 1.5 kb of LAT (and its promoter) at a distant site completely restored in vivo spontaneous reactivation to wild type levels, despite the remaining inability of the original LAT genes to transcribe any LAT RNA. The function of LAT involved in efficient spontaneous reactivation therefore appeared to map completely within the first 1.5 kb of the LAT gene.