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Early effects of dimethylnitrosamine on protein chain initiation and postmicrosomal polyadenylic acid-containing RNA
Abstract:
A mouse liver S-30 system was used to study the early effects of dimethylnitrosamine (DMNA) on polypeptide chain initiation and messenger RNA content. The inhibition of protein synthesis after DMNA administration was associated with a reduced capacity of the S-30 system to form 80S ribosomal initiation complexes. The binding of formylatable methionyl transfer RNA to polysomes was also depressed. The initiation defect was detectable in the assay system slightly later than the decrease in protein synthesis. Addition of mRNA stimulated both translation and 80S initiation complex formation but could not fully restore the activity of the S-30 system from DMNA-treated mice. A loss of poly(A)+ RNA from the postmicrosomal subfraction of the S-30 fraction was observed as early as 15 min after DMNA administration. Later, polyriboadenylic acid also decreased in the microsomal fraction. Monosomes accumulating in response to DMNA treatment were deficient in mRNA as measured by polyriboadenylic acid analysis. Conversely, the proportion of polyriboadenylic acid in the remaining polysomes increased, indicating that the mRNA had become less densely occupied with ribosomes.
Insights
Dimethylnitrosamine (DMNA) impairs liver protein synthesis by inhibiting polypeptide chain initiation. This occurs due to reduced messenger RNA (mRNA) binding to ribosomes and a loss of poly(A)+ RNA.
Area of Science:
- Biochemistry
- Molecular Biology
- Toxicology
Background:
- Dimethylnitrosamine (DMNA) is a potent hepatotoxin.
- Understanding DMNA's molecular mechanisms is crucial for predicting its toxicity.
Purpose of the Study:
- To investigate the early effects of DMNA on protein synthesis initiation and messenger RNA (mRNA) content in mouse liver.
- To elucidate the molecular basis of DMNA-induced inhibition of protein synthesis.
Main Methods:
- Utilized a mouse liver S-30 cell-free system.
- Assessed polypeptide chain initiation, 80S ribosomal initiation complex formation, and mRNA content.
- Measured the binding of formylatable methionyl transfer RNA to polysomes.
- Analyzed poly(A)+ RNA and polyriboadenylic acid levels in different cellular fractions.
Main Results:
- DMNA inhibited protein synthesis by reducing the formation of 80S ribosomal initiation complexes.
- The binding of formylatable methionyl transfer RNA to polysomes was depressed.
- A significant loss of poly(A)+ RNA was observed in the postmicrosomal and microsomal fractions.
- Accumulated monosomes were deficient in mRNA, and polysomes showed decreased ribosome occupancy.
Conclusions:
- DMNA disrupts liver protein synthesis primarily by impairing polypeptide chain initiation.
- The observed defects in initiation are linked to reduced mRNA binding and poly(A)+ RNA degradation.
- These molecular alterations provide insight into DMNA's early toxic effects on cellular translation.