Miscoding by Escherichia coli tRNAs for Methionine, Cysteine and Valine in the Synthesis of Rabbit Globin

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Abstract
Methionine, valine and cysteine tRNAs from E. coli have been used in the reticulocyte transfer system and the products of transfer investigated. Fractionated methionine tRNAF and methionine tRNAM both transfer methionine into the two methionine containing peptides in rabbit globin, and also transfer it into other peptides not corresponding to globin peptides. Little difference was observed in the patterns of transfer of methionine tRNAF and methionine tRNAM. The occurrence of the extra peptides is thought to be due to miscoding by the methionine tRNAs for valine positions coded by GUG. Valine tRNA transfers mainly into globin peptides, but some valine is transferred in non‐globin peptides. αT1 and βT1 both receive valine from E. coli valine tRNA, so that no special valine tRNA can be required for the initiation of globin chains. Cysteine tRNA transferred no detectable cysteine into the two cysteine containing peptides, but it did transfer cysteine into some arginine positions. From a consideration of the patterns of miscoding it has been possible to make tentative codon assignments for certain valine and arginine positions of rabbit globin. Possible causes of miscoding by E. coli tRNA in the reticulocyte transfer system are discussed.