Klaus Harbers

Nucleotide clusters in deoxyribonucleic acids. XII. The distribution of 5-methylcytosine in pyrimidine oligonucleotides of mouse L-cell satellite DNA and main band DNA.

Abstract Mouse L-cell DNA radioactively labeled in the 5-methylcytosine (5-MeC) residue was fractionated into satellite and main band DNA. Satellite DNA was found to contain about four times the molar concentration of 5-MeC than the main band DNA. Based on the known 5-MeC content of total L-cell DNA it was calculated that satellite DNA contains 3.5 – 4.6% 5-MeC. Both DNA fractions were depurinated and the pyrimidine oligonucleotides released separated by ionophoresis-homochromatography. In satellite DNA 5-MeC is distributed non-randomly. About 40% of the total 5-MeC is present in the sequence Pu - 5-MeC - Pu. The remainder occurs in the oligonucleotides CT, CT3, C2T4, C2T5 and C3T5 only. The distribution of 5-MeC in main band DNA differs from that in satellite DNA indicating that two different fractions of the same nuclear DNA are methylated in different sequences.

Nucleotide clusters in deoxyribonucleic acids. X. Sequences of the pyrimidine oligonucleotides of mouse L-cell satellite DNA

Summary All the major pyrimidine oligonucleotides from the light and heavy strands of mouse L-cell satellite DNA have been sequenced. The sequences within each strand show a close homology with each other. In the heavy strand thymines predominate at the 5′-ends and cytosines at the 3′-ends and the longest pyrimidine tracts are the two octamers T-T-T-T-C-C-T-C and C-T-T-T-T-T-T-C. The hexamers T-T-T-T-C-C, T-T-T-C-T-C and T-T-T-T-T-C occur most frequently and their sequence homology with each other and the rest of the pyrimidine oligonucleotides of the heavy strand suggests that the basic repeating unit contained a pyrimidine hexamer. In the light strand sequence homologies and frequency of occurrence of C-T-T suggest the basic repeating unit also contained a pyrimidine trimer. These conclusions support the theory that mouse satellite DNA consists of a short repeating unit which has undergone several base changes during evolution.

The S13 Genome

Bacteriophage S13, one of the isometric phages, was first described by Burnet (1927) as one of a series of phages isolated from Salmonella cultures; these phages were given the prefix S followed by arabic numerals. Soon after its discovery S13 was found to have anomalous properties in comparison with the other phages. For example, it was shown to migrate to the cathode in an electric field, and this electrical behavior was strikingly affected by changes in pH (Burnet and McKie 1930). It was relatively stable to reducing dyes and diffused much more rapidly than other phages. The latter result led to the speculation that S13 was smaller than most other phages (Burnet and McKie 1930). Evidence to support this hypothesis came from early centrifugal studies by Elford (1936), and an estimate was made of its size as 15 to 17 nm—a figure in agreement with results from previous ultrafiltration analyses (Elford and Andrewes 1932). Subsequent studies concentrated mainly on the action of various compounds on S13 (S13 having been chosen as a test phage because of its small size). One study revealed the unusual result that, unlike other phages, when S13 was irradiated by ultraviolet light it failed to kill its host (Mills 1955). In 1958, Zahler published a comparison of some of the biological properties of S13 and the more recently discovered ϕ X174; a close serological relationship between the two phages was found. In 1959, I. Tessman showed by 32 P-decay studies that the DNA of phage S13 is...