Identification and characterization of a 50K DNA-binding protein of guinea-pig cytomegalovirus.

In a previous study we showed that cells infected with guinea-pig cytomegalovirus (GPCMV) contain large amounts of a non-structural 50K nuclear protein that is detectable by immunoelectron microscopy using monoclonal antibodies. The present study shows that this 50K protein is a DNA-binding protein, as determined by single-stranded DNA affinity chromatography, and a phosphorylated protein as demonstrated by immunoprecipitation using [32P]orthophosphate-labelled cells. This protein binds both viral and host cellular double-stranded and single-stranded DNA, assayed by a simple method using DNA linked to a nylon membrane. Induction of the 50K protein in GPCMV-infected cells was highly dependent on viral DNA synthesis, which was detected by dot hybridization using a cloned GPCMV DNA probe. Synthesis of the 50K protein was significantly impaired when phosphonoacetic acid was added to the culture medium. Induction of the 50K protein was detected about 6 h before the appearance of the 76K viral matrix protein.