i.e. rare bases — 5-methylcytosine, 5-hydroxymethylcytosine, 2-methyl-
aminopurine, 6-methylaminopurine, etc. (Fig. 2–47) were discovered.
These bases lead to errors in the binding to other bases and exert an
influence on the replication and translation processes. Minor bases are also
found in RNA.
The road to the heterogeneous character of DNA is open. The
assumption that the eukaryotic cells contain much more genetic material
than it is needed according to the calculations made and the absence of
correlation between the complexity of a given organism and the size of
its genome was confirmed experimentally. Using the methods of
denaturation, hybridization and reassociation of DNA, the presence of
unique and reoeated nucleotide sequences was established as well as
the so-called satellite DNA.
For the first time a satellite DNA-component was observed by Kit
(1961) upon centrifugation of mouse DNA in neutral density gradient of
CsCl. Kit has established that about 10% of it is found in the light band
(p=1.691 g.cm³) compared to the major zone (p=1.700 g.cm³), which is
due to the decreased G—C content. A characteristic feature of this
fraction is that it differs in its nucleotide composition from the rest of the
major part of DNA. Satellite components are also found in many other
eukaryotic cells. In some species they comprise more than 30% of the
total amount of nuclear DNA, varying in nucleotide composition.