摘要：

Two new constituents of the acid-soluble fraction of phage particles have been studied. One is a polypeptide composed chiefly of aspartic and glutamic acids and lysine, representing about 1% of the total carbon of the particles, and weighing perhaps 4 × 10 −12 μg per particle. The second, called substance A, remains unidentified. It is a low molecular weight substance, contains about 1.5% of the total carbon of the particles, and is chiefly characterized by the fact that it receives much of its carbon from arginine supplied in the culture medium (also containing glucose), but does not yield arginine on hydrolysis. The two substances can be specifically traced as acid-soluble C 14 derived from lysine or arginine, respectively, which permits experimentation along the lines indicated below. The polypeptide is not synthesized simultaneously with phage-precursor deoxyribonucleic acid (DNA) formed in the presence of chloramphenicol. Neither is it transmitted as such along with the DNA from parental to offspring phage particles. These facts are interpreted to mean that the acidsoluble peptide is not an essential constituent of the phage chromosome. Substance A is formed in the presence of chloramphenicol and is transmitted unchanged from parental to offspring phage. However, it can also be assimilated from the culture medium by infected bacteria, and reappears as substance A in the issue of phage particles. Moreover, substance A in the culture medium interferes with the transfer of parental substance A, but not with the transfer of parental DNA, into offspring. Hence it is concluded that substance A also is not an essential constituent of the phage chromosome. Finally, technically improved experiments show that the tail of the phage particle does not contain more than 2 × 10 −12 μg of protein that is efficiently transferred from parental to offspring phage. The over-all conclusion is reached that if the phage chromosome contains any non-DNA constituents, these must represent appreciably less than 1% of the total phage carbon, or not more than 10 −12 μg of carbon per particle. Such a component would comprise only about 1% of the mass of the DNA.

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