Immunological characterization of the low-molecular-weight DNA binding protein of mouse mammary tumor virus.

p14, a low-molecular-weight MMTV protein previously identified as having DNA-binding properties and encoded by the gag region of the MMTV genome, was purified by affinity chromatography on DNA-sepharose. Immunological characterization of the purified protein showed that MMTV p14 shares no cross-reactivity with gp52, gp36 and p10, antigens associated with the MMTV envelope, nor with p27 antigen found in the virion core. Purified MMTV p14 did show cross-reactivity with purified intracytoplasmic A particles, supporting the concept that A particles are morphological precursors to MMTV cores. In addition, shared antigenic determinants between intracytoplasmic A particles and MMTV p27, p20 and p10 were demonstrated. MMTV p14 did not cross-react with the low-molecular-weight DNA-binding proteins of MuLV or of type-C or -D viruses of higher mammals.