Identification and Characterization of the UL37 Protein of Herpes Simplex Virus Type 1 and Demonstration that it Interacts with ICP8, the Major DNA Binding Protein of Herpes Simplex Virus
Uniformed Services University Of The Health Sciences Bethesda United States
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We have identified and characterized the previously unknown protein encoded by the UL37 gene in HSV-1-infected cells. Using in vitro transcription and translation of the UL37 gene, we have generated a UL37-specific antiserum to identify the UL37 protein in HSV-1-infected cells. The UL37 protein has an apparent molecular weight of 120 kD based on its migration on 50S-polyacrylamide gels and is indistinguishable by immunoblot analysis from the UL37 protein expressed by a vaccinia recombinant. By time course experiments and use of a DNA synthesis inhibitor, we have demonstrated that the UL37 protein is expressed prior to the onset of DNA synthesis, but requires viral DNA synthesis for maximum expression. Based on these results, we have classified the UL37 gene as belonging to the gamma 1 class of HSV genes. Analysis of purified virions failed to detect the UL37 protein, demonstrating that it is a nonstructural protein. Analysis of HSV-1-infected cell proteins by single-stranded and double-stranded chromatography demonstrated that the UL37 protein exhibits a high affinity DNA binding activity, co-eluting with the HSV-1 major DNA binding protein, ICP8. ICP8 is an essential, multifunctional viral protein, involved in viral DNA replication and late gene regulation. We have compared the DNA binding activities and nuclear localization of the UL37 proteins derived from cells infected with HSV-1, an HSV-1 recombinant d21 containing a deletion in the ICPS gene, and a vaccinia recombinant containing the UL37 gene. These studies demonstrated that the expression of UL37 in the presence of a functional ICPS protein is required for the observed DNA binding activity and nuclear localization of the UL37 protein in HSV-1 infected cells. Therefore, the UL37 and ICPS proteins form a complex in HSV-1-infected cells.