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Structure of the mouse mammary tumor virus: characterization of bald particles
Abstract:
The polypeptide, antigenic, and morphological structure of the mouse mammary tumor virus was studied following protease digestion of intact virions. Intact, untreated virions (rho = 1.17 g/ml) had characteristic envelope spikes, five major polypeptides, and were precipitated by antisera against gp52. Two of the major polypeptides, with molecular weights of 52,000 (gp52) and 36,000 (gp36), had carbohydrate moieties. Protease treatment resulted in spikeless, "bald" particles (rho = 1.14 g/ml), which had altered surface antigenicity and which contained neither gp52 nor gp36. These data indicated that gp52 and gp36 were on the viral envelope. Bald particles retained a 28,000 dalton polypeptide (p28) which was proposed as the major internal polypeptide.
Insights
Researchers investigated the mouse mammary tumor virus structure using protease digestion. Key envelope proteins gp52 and gp36 were identified and removed, revealing the internal polypeptide p28.
Area of Science:
- Virology
- Molecular Biology
- Immunochemistry
Background:
- The mouse mammary tumor virus (MMTV) is an important retrovirus studied for its role in cancer.
- Understanding the structural composition of MMTV virions is crucial for developing targeted therapies.
Purpose of the Study:
- To elucidate the polypeptide, antigenic, and morphological structure of MMTV.
- To identify the location and function of key viral proteins, particularly those on the envelope.
Main Methods:
- Protease digestion of intact MMTV virions.
- Analysis of viral polypeptides using molecular weight determination.
- Immunoprecipitation using antisera against specific viral proteins.
- Density gradient centrifugation to characterize viral particles.
Main Results:
- Intact MMTV virions exhibited characteristic envelope spikes and contained five major polypeptides, including glycosylated gp52 and gp36.
- Protease treatment yielded "bald" particles lacking envelope spikes, gp52, and gp36, indicating their surface localization.
- These "bald" particles retained a 28,000 dalton polypeptide (p28), identified as the major internal protein.
Conclusions:
- The viral envelope proteins gp52 and gp36 are essential components of the MMTV virion surface.
- Protease digestion effectively removes envelope proteins, exposing the internal viral structure.
- The polypeptide p28 is proposed as the primary internal structural protein of MMTV.