Bacterial expression of the capsid antigen domain and identification of native gag proteins in spumavirus-infected cells.

A bacterial expression plasmid containing the central part of the gag gene of the human spumaretrovirus (HSRV) was constructed and expressed in E. coli. The expected protein product consisting of the complete region of the HSRV capsid antigen and part of the matrix protein was expressed in relatively large amounts. Polyclonal antisera raised against this recombinant protein were used to identify authentic gag precursors of 78 and 74 kDa and processed gag proteins of 60, 58, and 33 kDa in HSRV-infected human embryonal fibroblast cells by radioimmunoprecipitation. The recombinant antigen will be useful for the detection of antibodies against HSRV gag proteins in human sera.