Effect of lead on globin mRNA in vivo and in vitro

Plumbous ion has been shown to be a potent catalyst for the depolymerization of RNA in vitro but the question of whether or not Lead-catalyzed RNA degradation also occurs in vivo has never been addressed. Our experimental design, to answer this question, was to transfuse rabbit reticulocytes into normal rabbits and rabbits that had been injected with different doses of lead acetate. After 24 hours the mRNA was isolated form the reticulocytes of each rabbit by phenol extraction and affinity chromatography on oligo dT cellulose. The amount of mRNA per ml of packed reticulocytes was determined. The integrity of the mRNA was then determined with a cell-free reticulocyte translation system that was dependent on exogenous mRNA. The results showed that there was little difference in the amount of mRNA recovered from control and treated rabbits, but the ability of the mRNA to support globin synthesis was decreased by as much as 86% in the lead-treated rabbits. These data suggest that not only is mRNA attacked by lead in vivo but that the lead attacks the mRNA at just one or at least very few sites. In the in vivo studies, purified rabbit globin mRNA was incubated with lead acetate and the products of this reaction were labelled with {sup 32}P using T4 polynucleotide kinase. A labelled fragment of slightly greater mobility than tRNA was isolated by gel electrophoresis. This fragment was digested to the monomers and analyzed by TLC to identify the nucleotide at the 5' end.