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Further characterization of intracytoplasmic A particle-associated DNA
Abstract:
A DNA species with buoyant densities greater than mouse cellular DNA was found associated with intracytoplasmic A particles (CAP) isolated from mouse mammary tumor virus-infected mouse mammary tumors and mouse Leydig cell tumors which produce CAP but no complete mouse mammary tumor virus virions. This DNA species was absent in identically prepared tissue fractions from tumors which did not contain CAP. Treatment of CAP-associated DNA with pancreatic RNase A did not alter the buoyant density although a reduction in apparent molecular weight (broadening of the DNA band at equilibrium) was observed upon analytical equilibrium sedimentation in CsCl. The molecular weight of untreated CAP-associated DNA was estimated to range from 0.8 x 10(6) to 3.1 x 10(6). Base composition analysis showed CAP-DNA to possess an approximate guanine plus cytosine content of 38%. Ninety percent of CAP-associated DNA eluted as single-stranded molecules upon hydroxyapatite column chromatography, a characteristic that accounts in part for its higher buoyant density in neutral CsCl compared to native double-stranded mouse DNA. In two preparations, CAP-DNA had a sedimentation coefficient of 7 to 8S.
Insights
A novel DNA species was discovered associated with intracytoplasmic A particles (CAP) in mouse tumors. This unique DNA, distinct from mouse cellular DNA, was absent in tumors lacking CAP, suggesting a specific link.
Area of Science:
- Molecular Biology
- Virology
- Oncology
Background:
- Intracytoplasmic A particles (CAP) are found in various mouse tumors, including those infected with mouse mammary tumor virus (MMTV).
- The molecular composition of CAP, particularly any associated nucleic acids, remains incompletely understood.
Purpose of the Study:
- To investigate the presence and characteristics of DNA associated with intracytoplasmic A particles (CAP).
- To determine if this DNA species is specific to CAP-containing tumors.
Main Methods:
- Isolation of CAP from MMTV-infected mammary tumors and Leydig cell tumors.
- Buoyant density centrifugation in CsCl to analyze DNA properties.
- Analytical equilibrium sedimentation and hydroxyapatite column chromatography to assess DNA structure and purity.
- RNase A treatment to evaluate RNA content.
Main Results:
- A distinct DNA species, denser than mouse cellular DNA, was found associated with CAP.
- This CAP-associated DNA was absent in tumors lacking CAP.
- The DNA was primarily single-stranded, with an estimated molecular weight between 0.8 x 10^6 and 3.1 x 10^6.
- Base composition analysis revealed a guanine-cytosine content of approximately 38%.
Conclusions:
- A unique, single-stranded DNA species is specifically associated with intracytoplasmic A particles (CAP).
- This finding suggests a potential role for this DNA in CAP formation or function within specific tumor types.
- Further research is warranted to elucidate the origin and biological significance of CAP-associated DNA.