[Distribution of pyrimidine blocks in the DNA of Brevibacterium linens, Arthrobacter globiformis, Nocardia corallina and Nocardia rubra].

The nucleotide composition and the frequency of pyrimidine blocks were studied in DNA of the following bacteria: Brevibacterium linens (Weignamm, 1910) Breed, 1953; Arthrobacter globiformis (Conn, 1928) Conn et Dimmick, 1947; Nocardia corallina (Bergey et al., 1923) Waksman et Henrici, 1948; Nocardia rubra (Krassilnikov, 1949) Waksman et Henrici, 1948. These organisms are classed by some microbiologists as mycobacteria (the Mycobacteriaceae family) while other authors regard them as representatives of three families belonging to two orders. About 60 percent of all pyrimidines in DNA of these bacteria are found in the sequences pur-pyr-pur and pur-pyr-pyr-pur, the number of dipyrimidines being higher than the amount of monopyrimidine nucleotides. The content of dipyrimidine nucleotides in DNA of Nocardia corallina and Nocardia rubra is higher (16.8 mole %) than the content of dipyrimidine blocks in DNA of Brevibacterium linens and Arthrobacter globiformis, in which the quantity of dipyrimidines is almost the same (13.9 and 14.4 mole %). A new characteristic, the selected mean value, is suggested to evaluate differences in the distribution of pyrimidines in DNA.