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Synthesis and processing of precursor polypeptides to murine mammary tumor virus structural proteins
Abstract:
Biosynthesis of murine mammary tumor virus (MuMTV) proteins was studied in the chronically MuMTV-infected epithelial cell line MuMT-73 by using monospecific antisera to the major MuMTV core protein p27 and the major envelope glycoprotein gp47. In pulse-labeling experiments using [35S]methionine, monospecific antisera to p27 precipitated a 75,000-molecular-weight protein as the major intracellular component. Analysis of the same cellular extracts with monospecific antisera to gp47 revealed that the gp47 precursor was a 70,000-dalton protein. After chase periods, there was a loss of label from the precursors and a concomitant increase of labeled extracellular mature viral proteins. The glycoprotein precursor incorporated labeled glucosamine and seemed to be processed more rapidly than the p27 precursor. Considerable amounts of apparently nonvirion-associated gp47 and glycoprotein precursor could be detected in the extracellular culture fluid.
Insights
Murine mammary tumor virus (MuMTV) protein biosynthesis was investigated. Researchers identified precursor proteins for MuMTV core protein p27 and envelope glycoprotein gp47, tracking their maturation and extracellular release.
Area of Science:
- Virology
- Molecular Biology
- Cell Biology
Background:
- Murine mammary tumor virus (MuMTV) is an oncogenic retrovirus.
- Understanding MuMTV protein biosynthesis is crucial for studying viral replication and pathogenesis.
Purpose of the Study:
- To investigate the biosynthesis of major MuMTV core protein p27 and envelope glycoprotein gp47.
- To characterize the precursor proteins and their processing pathways.
Main Methods:
- Utilized monospecific antisera against p27 and gp47.
- Employed pulse-labeling with [35S]methionine and [3H]glucosamine.
- Analyzed protein precursors and mature viral proteins in infected epithelial cells (MuMT-73).
Main Results:
- Identified a 75,000-dalton intracellular precursor for p27.
- Identified a 70,000-dalton precursor for gp47, which incorporated glucosamine.
- Observed processing of precursors into mature extracellular viral proteins after chase periods.
- Noted faster processing of the gp47 precursor compared to the p27 precursor.
- Detected significant amounts of extracellular nonvirion-associated gp47 and its precursor.
Conclusions:
- Elucidated the precursor forms and processing of key MuMTV structural proteins.
- Demonstrated differential processing rates between p27 and gp47 precursors.
- Highlighted the extracellular presence of nonvirion-associated gp47, suggesting alternative secretion pathways or roles.