Nucleic acids are acidic in nature and stain with basic dyes, such as toluidine blue, pyronin and methyl green. These specific staining agents are used for locating nucleic acids in various parts of the cell. DNA after hydrolysis reacts with Schiff’s reagents to give a purple color (Feulgen reaction).

Eucaryotic DNA is always associated with proteins and RNA, and the term chromatin is used to designate this complex material. Proteins in association with chromosomes are of two types: histones and non-histones. Histones are basic proteins, rich in lysin and arginine residues, and usually linked to phosphate groups by ionic bonds. They are supposed to act as nonspecific genetic repressors which block the transcription of DNA segments to which they are attached.

Non-histones are chromosomal proteins consisting of diverse types of molecules. These have a functional role and include many important enzymes, such as polymerases, methylases, kinases, phosphatases, etc. The non-histone proteins represent active chromatin material and participate in gene regulation and transcriptional  activity. The amount of RNA associated with chromatin is very small, roughly 3%, consisting o f nascent RNA chains. On the other hand, procaryotic DNA is without any proteins.