Abstract
1. Alterations were observed in the ribosome complement of Staphylococcus aureus (strain Duncan), caused by 5-fluorouracil added during logarithmic growth in the presence of uracil. 2. The accumulation of particles (sedimentation coefficient 49.1 in 10 −2 M magnesium sulphate) characterised by ribonuclease (EC 2.7.7.16) sensitivity was noted. 3. General resistance of ribosomes to aggregation at high magnesium ion concentration was found, with only trace amounts of particles having sedimentation coefficients greater than 70 S in 10 −2 M magnesium sulphate. 4. Incorporation of [ 14C]leucine into the ribosomal fraction during logarithmic growth indicated that the initial stages of protein synthesis proceeded rapidly in the presence of 5-fluorouracil. 5. It was demonstrated that 5-fluorouracil blocked normal ribosome biosynthesis: that particles having abnormal sedimentation coefficients were produced, and that protein synthesis continued in the presence of the analogue. It was concluded that pre-existing ribosomes continued to function up to 60 min after 5-fluorouracil was added to the culture, and that structurally different, non-functional ribosomes were synthesized.
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