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Abstract:
The effects of Pb2+, a potent catalyst for the depolymerization of RNA have been studied on brome mosaic virus (BMV) RNA, rabbit globin m-RNA and polyuridylic acid. After exposure of these natural and synthetic messengers to a sufficiently high concentration of Pb2+, they all lost their ability to stimulate amino acid incorporation in cell-free protein-synthesizing systems. There were differences in the susceptibilities of the messengers; gloing the m-RNA for 40 min revealed that there was a threshold Pb2+ concentration below which no loss of m-RNA activity was observed. The threshold concentration was considerably greater than the Pb2+ concentration at which protein synthesis is inhibited in reticulocytes and overt symptoms of plumbism are observed. However, when m-RNA were incubated for an extended period (24 h), even with sub-threshold concentrations of Pb2+, there was destruction of messenger function and globin m-RNA was more susceptible than BMV-RNA. Also the susceptibility of m-RNA to Pb2+ is temperature-dependent, which would indicate that m-RNA, like t-RNA, exists as a population of molecules in different conformational states that are not readily interconvertible.