The incorporation of [14C]amino acids into the acid precipitable material of chick embryo fibroblasts was inhibited by both sparsomycin and gougero- tin with an efficiency which varied according to the amino acid and to the antibiotic. Of 16 amino acids tested, proline was the most susceptible to the action of sparsomycin and phenylalanine was the most resistant. With gougerotin, the order of decreasing susceptibilities of four amino acids were: phenylalanine, proline and glycine, lysine. Inhibition of virus growth by the two antibiotics was also specific. Synthesis of pseudorabies virus was very susceptible to inhibition by sparsomycin, while vaccinia virus synthesis was almost completely resistant. Newcastle disease virus, fowl plague and Western equine encephalomyelitis viruses showed intermediate susceptibilities to that drug.
In contrast, the synthesis of fowl plague virus was much more inhibited by gougerotin than that of Newcastle disease virus, and this antibiotic had an equal action on the growth of pseudorabies and vaccinia viruses. Most of the results may be explained by assuming that sparsomycin is an effective inhibitor of the activity of virus messenger RNAs which are rich in guanine and cytosine, while gougerotin is more effective on uracil-rich virus messenger RNAs.
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