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Intracytoplasmic A particles: mouse mammary tumor virus nucleoprotein cores?
Abstract:
A rapid method for the isolation of intracytoplasmic A particles, the putative intracellular nucleoprotein cores of mouse mammary tumor virus (MTV), is presented. Spontaneous C3H/He mouse mammary tumors and transplantable mouse Leydig cell tumor were used as source material. Large aggregations of intracytoplasmic A particles were separated from cellular contaminants on discontinuous sucrose gradients and subsequently further purified by isopycnic banding in linear sucrose gradients. The purified particles were solubilized in sodium dodecyl sulfate, and the structural proteins were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Purified mouse mammary tumor virions were solubilized, and their proteins were analyzed in the same way. Comparison of co-electrophoretic gels indicated a lack of correlation in the molecular size of the major structural proteins in intracytoplasmic A particles and MTV. The three major proteins of the A particles were calculated to be 80,000; 35,000; and 20,000 daltons. Five major polyacrylamide gel electrophoresis bands were obtained with purified MTV; these were 90,000; 69,000; 55,000; 37,000; and 27,500 daltons. These figures showed good correlation with those published for MTV by Nowinski et al. These results suggest the need for the reexamination of the current tenet that intracytoplasmic particles represent intracellular MTV nucleoprotein cores.
Insights
This study presents a new method for isolating mouse mammary tumor virus (MTV) A particles. Analysis reveals distinct protein profiles, challenging the idea that A particles are MTV nucleoprotein cores.
Area of Science:
- Virology
- Molecular Biology
- Oncology
Background:
- Intracytoplasmic A particles are hypothesized to be the intracellular nucleoprotein cores of mouse mammary tumor virus (MTV).
- Understanding the composition of these particles is crucial for elucidating MTV replication and pathogenesis.
Purpose of the Study:
- To develop a rapid isolation method for intracytoplasmic A particles.
- To compare the structural proteins of A particles with those of purified MTV.
- To re-evaluate the current understanding of the relationship between A particles and MTV.
Main Methods:
- Isolation of A particles from spontaneous mouse mammary tumors and Leydig cell tumors using discontinuous and linear sucrose gradient centrifugation.
- Solubilization of purified particles and virions using sodium dodecyl sulfate.
- Analysis of structural proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE).
Main Results:
- A rapid purification protocol for intracytoplasmic A particles was established.
- SDS-PAGE analysis revealed distinct molecular weights for the major structural proteins of A particles (80,000, 35,000, and 20,000 daltons) compared to MTV (90,000, 69,000, 55,000, 37,000, and 27,500 daltons).
- The protein profiles showed a lack of correlation between A particles and MTV.
Conclusions:
- The distinct protein compositions challenge the established tenet that intracytoplasmic A particles are the intracellular nucleoprotein cores of MTV.
- Further investigation is warranted to clarify the precise nature and origin of intracytoplasmic A particles in relation to MTV.