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Translatability of rat kidney mRNA after mercury administration
Abstract:
Young male rats received an intraperitoneal injection of 0.5 mg HgCl2/kg body weight and 16 h later the kidneys were removed and homogenized to prepare the polysomal fraction from which the poly(A)+ RNA was obtained. The activity of this fraction was assessed by translating the poly(A)+ RNA in a mRNA-dependent rabbit reticulocyte lysate and the activity was markedly elevated relative to preparations from control rat kidneys. The incorporation of labelled leucine and cysteine, but not phenylalanine, into a low molecular weight protein (approximately 10 000 as judged by denaturing polyacrylamide gel electrophoresis) accounted for the increased mRNA activity. The mobility during electrophoresis of the denatured labelled product and carboxymethylated product, as well as their acidic isoelectric points, provided evidence that it is metallothionein mRNA which exhibits increased translatability in preparations derived from mercury-treated rats.
Insights
Mercury exposure significantly increases the translatability of metallothionein mRNA in rat kidneys. This suggests a rapid cellular response to heavy metal toxicity, enhancing the production of protective proteins.
Area of Science:
- Biochemistry
- Toxicology
- Molecular Biology
Background:
- Mercury chloride (HgCl2) is a nephrotoxic heavy metal.
- Kidney cells possess defense mechanisms against toxic insults.
- Metallothioneins are proteins known to bind heavy metals.
Purpose of the Study:
- To investigate the effect of mercury exposure on kidney mRNA activity.
- To identify specific mRNA species whose translatability is altered by mercury.
Main Methods:
- Young male rats were injected with mercury chloride (HgCl2).
- Kidney polysomal fractions and poly(A)+ RNA were isolated.
- In vitro translation assays using rabbit reticulocyte lysate were performed.
- Analysis of synthesized proteins using polyacrylamide gel electrophoresis and isoelectric focusing.
Main Results:
- Poly(A)+ RNA from mercury-treated rat kidneys showed markedly elevated translational activity.
- Increased activity was attributed to the synthesis of a low molecular weight protein (approx. 10,000 Da).
- Incorporation of labeled leucine and cysteine, but not phenylalanine, indicated the protein's composition.
- Electrophoretic and isoelectric properties strongly suggested the protein is metallothionein.
Conclusions:
- Mercury exposure rapidly enhances the translatability of metallothionein mRNA in rat kidneys.
- This suggests an immediate transcriptional or post-transcriptional response to protect against mercury toxicity.
- The findings highlight a specific molecular mechanism involved in heavy metal detoxification.