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Structural analysis of the intracellular RNAs of murine mammary tumor virus
Abstract:
We have characterized murine mammary tumor virus (MuMTV)-specific RNA in several types of cells in which viral DNA is transcribed into RNA: cultured GR mouse mammary tumor cells, S49 lymphoma cells from BALB/c mice, lactating mammary glands from C57BL/6 mice, and mink lung cells infected in vitro with MuMTV. In all cell types studied, there are three distinct species of intracellular viral RNA, with sedimentation coefficients of 35S, 24S, and 13S (or molecular weights of 3.1 X 10(6), 1.5 X 10(6), and 0.37 X 10(6), as determined by rate-zonal sedimentation in sucrose gradients and by electrophoresis in agarose gels under denaturing conditions. These three viral RNA species appear to be present regardless of viral RNA concentration, responsiveness to glucocorticoid hormones, production of extracellular virus, and use of either endogenous or acquired MuMTV proviral DNA as template. The three viral RNAs display characteristics of mRNAs in that they are polyadenylated, associated with polyribosomes, and released from polyribosomes by treatment with EDTA; hence all three species presumably direct the synthesis of virus-coded proteins. The two larger species of viral RNA are probably responsible for synthesis of the structural proteins of the virion, but the function of the 13S RNA is not known. Both of the subgenomic RNAs contain sequences found at the 3' terminus of 35S (or genomic) RNA. However, only the 24S RNA (not the 13S RNA) contains sequences which are located at the 5' terminus of 35S RNA and are apparently transposed during RNA synthesis of maturation, as described for subgenomic mRNA's of other retroviruses.
Insights
Murine mammary tumor virus (MuMTV) produces three distinct intracellular RNA species (35S, 24S, and 13S). These RNAs are polyadenylated and associated with ribosomes, suggesting they function as messenger RNAs (mRNAs) for protein synthesis.
Area of Science:
- Virology
- Molecular Biology
- Genetics
Background:
- Murine mammary tumor virus (MuMTV) is a retrovirus implicated in mammary tumorigenesis in mice.
- Understanding the transcription and processing of viral RNA is crucial for deciphering viral replication and pathogenesis.
Purpose of the Study:
- To characterize the intracellular MuMTV-specific RNA species present in various cell types.
- To investigate the properties and potential functions of these viral RNA molecules.
Main Methods:
- Rate-zonal sedimentation in sucrose gradients to determine sedimentation coefficients.
- Agarose gel electrophoresis under denaturing conditions to assess molecular weights.
- Analysis of polyadenylation, association with polyribosomes, and 5'/3' terminal sequences.
Main Results:
- Three distinct intracellular MuMTV RNA species (35S, 24S, and 13S) were identified across different cell types.
- These RNAs exhibit characteristics of messenger RNAs (mRNAs), including polyadenylation and association with polyribosomes.
- Both 24S and 13S RNAs contain sequences from the 3' terminus of the genomic 35S RNA.
- Only the 24S RNA contains sequences from the 5' terminus of the 35S RNA, suggesting specific processing or transposition.
Conclusions:
- MuMTV utilizes multiple viral RNA species for gene expression, analogous to other retroviruses.
- The 35S RNA likely serves as genomic RNA and precursor for smaller RNAs.
- The 24S RNA is a subgenomic mRNA likely encoding structural proteins, while the function of the 13S RNA remains undetermined.