THE REGION OF THE HERPES-SIMPLEX VIRUS TYPE-1 LAT GENE INVOLVED IN SPONTANEOUS REACTIVATION DOES NOT ENCODE A FUNCTIONAL PROTEIN

We previously showed that the LAT function required for efficient spon taneous reactivation of herpes simplex virus type 1 (HSV-1) from neuro nal latency in the rabbit maps within the first 1.5 kb of the 8.3-kb p rimary LAT transcript. This demonstrated that LAT does not function vi a an antisense mechanism, since the first 1.5 kb of LAT does not overl ap any other known HSV-1 gene. Furthermore, if LAT encodes a protein e ssential for efficient spontaneous reactivation, it must map within th e functional first 1.5 kb of LAT. Thus, the absence of a well-conserve d LAT open reading frame in this region among all HSV-1 LAT genes capa ble of supporting high levels of spontaneous reactivation would demons trate that LAT does not encode a protein essential for efficient spont aneous reactivation. In this report, we sequenced the first 1.5 kb of LAT from HSV-1 McKrae, a strain with a very high spontaneous reactivat ion rate. Of the HSV-I LAT sequences available for comparison (17syn+, KOS, and Fl, only strain 17syn+ has a high spontaneous reactivation r ate. However, as shown in this report, a chimeric virus containing the KOS LAT gene on an HSV-I McKrae genetic background had a spontaneous reactivation rate indistinguishable from McKrae (15 versus 13.6%; P > 0.05). Thus, the spontaneous reactivation competency of the LAT gene f rom HSV-1 KOS was similar to that of the McKrae LAT gene. Comparative sequence analysis of the LAT genes from McKrae, 17syn+, and KOS reveal ed that none of the eight potential McKrae LAT ORFs were well conserve d. Additional types of sequence analyses further confirmed that none o f the potential ORFs were likely to encode a functional LAT protein. T hese results strongly support the notion that the LAT function involve d in spontaneous reactivation is mediated by a direct DNA or RNA mecha nism rather than a protein. (C) 1998 Academic Press.