Human cytomegalovirus strain Towne pp28 gene: sequence comparison to pp28 of HCMV AD169 and stable expression in Chinese hamster ovary cells.

Human cytomegalovirus (HCMV) contains a 28-kDa (pp28) matrix phosphoprotein which has been shown to be highly immunogenic in humans. We have cloned and sequenced the gene encoding pp28 of HCMV Towne strain (pp28Towne) and have expressed this gene in stable Chinese hamster ovary (CHO) cell lines in order to examine the structural, functional, and antigenic properties of this protein. The pp28Towne gene had 99% nucleotide and 98.4% amino acid similarity to the pp28 gene of HCMV AD169 strain (pp28AD169). We identified three amino acid substitutions (Gly70 to Ser70, Ser76 to Asn76, and Thr85 to Ala85) in pp28Towne, all clustered in a short 16 amino acid stretch located in the N-terminal half of the protein. The pp28Towne gene was expressed in CHO cells using a vector in which transcription was driven by a human beta-actin promoter. The expressed protein, having an electrophoretic mobility similar to that of HCMV-derived pp28, reacted strongly in immunoblot analysis with pp28-specific murine monoclonal antibodies as well as HCMV-seropositive human sera.