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Tritiated uridine is incorporated into the deoxyribonucleic acid of Bacillus subtilis and bacteriophage SPP1; the tritium is recovered in the cytidine moiety of both deoxyribonucleic acids.

Addition of the tryptophan analogues 5-methyl-tryptophan, 5-hydroxy-tryptophan, and 7-aza-tryptophan, during tryptophan starvation of a tryptophan auxotroph of Bacillus subtilis, stimulated amino acid incorporation. Two of the analogues tested, 5-methyl-tryptophan and 5-hydroxy-tryptophan, competed with each other, but their addition did not prevent tryptophan incorporation into acid-insoluble material. The incorporation of tryptophan and 5-hydroxy-tryptophan was stimulated when a mixture of phenylalanine and tyrosine was present in the medium. The two analogues 5-methyl-tryptophan and 5-hydroxy-tryptophan were recovered in protein hydrolysates of analogue-grown cultures, and there is evidence suggesting that the analogues are not chain terminators. Neither analogue prevented the polysome degradation that occurs during tryptophan starvation.

A decline in colony-forming ability is observed in actively growing cultures of a tryptophan arginine auxotroph of Bacillus subtilis after removal of tryptophan (tryptophanless death). This phenomenon can be prevented by simultaneous starvation of the other required amino acid or by chloramphenicol administered in bacteriostatic concentration but not by actinomycin. Addition of tryptophan analogues not only prevents the death but also allows recovery of the cells that have lost the ability to form colonies on solid media. The term tryptophanless death is therefore inappropriate. Chloramphenicol but not actinomycin inhibits the recovery brought about by tryptophan analogues.

Polysomes were extracted from Bacillus subtilis cells starved for a required amino acid. The monosome peak appeared soon after starvation; no difference in the rate of degradation was detected when the cells were starved for arginine or tryptophan in a double auxotroph. RNA production during starvation was not inhibited by actinomycin, but the molecular weight of the product made in the presence of the antibiotic was much lower. Indications that stable messenger ribonucleic acid is present for up to 90 min after amino acid starvation are also presented.

A survey was made of the capacity of competent cells of Bacillus subtilis to take up synthetic polynucleotides. Polydeoxyribonucleotides but not polyribonucleotides are taken up by the cells. Both types of polynucleotide failed to compete with transforming deoxyribonucleic acid in the transformation assay whereas both stimulated amino acid incorporation. The latter phenomenon appears to be nonspecific as there is no correlation between the codon composition of the polynucleotides employed and the amino acids whose incorporation was stimulated.

The decline in colony-forming ability observed during tryptophan starvation of Bacillus subtilis auxotrophs is a concentration-dependent phenomenon. It does not manifest itself when the initial cell concentration is 10(6) cells/ml or lower. This property has been used to test the killing activity of different fractions of the dying cells. Most of the activity recovered is found in the supernatant fluid of the starved culture. Sensitive and resistant strains can be identified. Active supernatant fluids can only be isolated from tryptophan auxotrophs sensitive to tryptophanless death. Resistant cells neither produce nor respond to the factor, and sensitive cells respond only when deprived of tryptophan. The killing activity is continuously produced and released into the medium at least up to 4 hr after removal of tryptophan from the culture. The killing activity is deoxyribonuclease-, ribonuclease-, and heat-resistant.