The UL37 open reading frame of the herpes simplex virus type 1 (HSV-1) DNA genome is located between map units 0.527 and 0.552. We have identified and characterized the UL37 protein product in HSV-1-infected cells. The presence of the UL37 protein was detected by using a polyclonal rabbit antiserum directed against an in vitro-translated product derived from an in vitro-transcribed UL37 mRNA. The UL37 open reading frame encodes for a protein with an apparent molecular mass of 120 kDa in HSV-i-infected cells; the protein's mass was assigned on the basis of its migration in sodium dodecyl sulfate-polyacrylamide gels. The UL37 protein is not present at detectable levels in purified HSV-1 virions, suggesting that it is not a structural protein. Analysis of time course experiments and experiments using DNA synthesis inhibitors demonstrated that the UL37 protein is expressed prior to the onset of viral DNA synthesis, reaching maximum levels late in infection, classifying it as a 'yl gene. Elution of HSV-1-infected cell proteins from single-stranded DNA agarose columns by using a linear KCI gradient demonstrated that the UL37 protein elutes from this matrix at a salt concentration similar to that observed for ICP8, the major HSV-1 DNA-binding protein. In addition, computer-assisted analysis revealed a potential ATP-binding domain in the predicted UL37 amino acid sequence. On the basis of the kinetics of appearance and DNA-binding properties, we hypothesize that UL37 represents a newly recognized HSV-1 DNA-binding protein that may be involved in late events in viral replication. * Corresponding author. in cells infected by HSV-1 in the presence of DNA synthesis inhibitors and therefore was initially identified as an early (,) transcript on the basis of the nomenclature at the time for the different temporal classes of HSV genes. In this study, we report on the identification and characterization of the UL37 protein from HSV-1-infected cells. Our results demonstrate that the UL37 ORF encodes a protein with an apparent molecular mass of 120 kDa, which is nonstructural, belongs to the-yl class of HSV genes, and binds to single-stranded (SS) DNA-agarose columns. A search of the predicted UL37 amino acid sequence reveals a potential ATP-binding site, and computer-assisted analysis comparing the UL37 sequence with the entire varicella-zoster virus (VZV) genome demonstrates that the VZV homolog, gene 21, shares 47% similarity at the amino acid level with UL37. While we currently have not identified a specific function for the UL37 protein, we hypothesize, on the basis of the results presented in this report, that the UL37 protein is a newly recognized HSV-1 DNA-binding protein which may play a role either in viral gene regulation or in the processing of newly synthesized viral DNA. MATERIALS AND METHODS Cells and viruses. Vero and CV-1 cells (American Type Culture Collection) and human thymidine kinase-negative (TK-) 143 cells were grown in Eagle's minimal essential medium supplemented with 10% (vol/vol) Serum-Plus (Hazleton Co...

The UL37 and ICP8 proteins present in herpes simplex virus type 1 (HSV-1)-infected-cell extracts produced at 24 h postinfection coeluted from single-stranded-DNA-cellulose columns. Experiments carried out with the UL37 protein expressed by a vaccinia virus recombinant (V37) revealed that the UL37 protein did not exhibit DNA-binding activity in the absence of other HSV proteins. Analysis of extracts derived from cells coinfected with V37 and an ICP8-expressing vaccinia virus recombinant (V8) and analysis of extracts prepared from cells infected with the HSV-1 ICP8 deletion mutants d21 and nlO revealed that the retention of the UL37 protein on single-stranded DNA columns required a DNA-binding-competent ICP8 protein.