REGULATION OF THE INITIATION OF HEMOGLOBIN SYNTHESIS IN THE BLOOD ISLAND CELLS OF CHICK EMBRYOS: III. QUALITATIVE STUDIES OF THE EFFECTS OF 8-AZAGUANINE AND PREPARATIONS OF TRANSFER RNAs

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Abstract
High concentrations of actinomycin D caused markedly greater inhibition of the incorporation of3H-uridine than concentrations adequate to totally inhibit synthesis of all RNAs of high molecular weight during short periods of incubation.8-Azaguanine markedly inhibited the formation of hemoglobin and the incorporation of leucine into protein by blastodiscs explanted prior to the 6-somite stage of development. This inhibition took place at later stages of development than the inhibition by actinomycin resulting in total arrest of messenger RNA synthesis. Inhibition of hemoglobin formation by 8-azaguanine was reversed by δ-aminolevulinic acid, without reversal of the inhibition of leucine incorporation.Preparations of amino-acylated bacterial transfer RNAs and of yeast and mammalian transfer RNAs partly or largely reversed the inhibition of hemoglobin formation by high concentrations of actinomycin. Preparations of "stripped" bacterial transfer RNAs were inactive. An active preparation of "charged" bacterial transfer RNA did not reverse inhibition of leucine incorporation by actinomycin. This preparation reversed the inhibition of hemoglobin formation by 8-azaguanine and partly reversed the inhibition of leucine incorporation due to the analogue.