The herpes simplex virus type 1 strain 17 open reading frame RL1 encodes a polypeptide of apparent M(r) 37K equivalent to ICP34.5 of herpes simplex virus type 1 strain F.

The region between the 'a' sequence and the 5' end of the IE1 gene within the long repeat sequence of the herpes simplex virus (HSV) genome plays an important role in the neurovirulence of both HSV-1 strain F and HSV-1 strain 17. However, there has been controversy over the protein-coding potential of this region. Although an open reading frame (ORF) was predicted in HSV-1(F) and shown to encode a polypeptide called ICP34.5, only recently has a corresponding ORF, designated RL1, been recognized in HSV-1(17). To determine whether the HSV-1(17) ORF is expressed, we raised antipeptide sera against predicted amino acid sequences from RL1; one serum specifically recognized a 37K protein in HSV-1(17)-infected cell extracts. Compared with the corresponding HSV-1(F) polypeptide the HSV-1(17) protein has a lower apparent M(r), shows similar kinetics of accumulation and intracellular localization but may accumulate to lower levels than the HSV-1(F) protein. The non-neurovirulent HSV-1(17) deletion variant 1716 fails to synthesize detectable levels of ICP34.5. Thus we have established that HSV-1(17), like HSV-1(F), expresses ICP34.5, a protein important for HSV neurovirulence.