Abstract
1. On the basis of susceptibility to digestion with dilute nucleases, the nine types of ribonucleoprotein (RNP) stainable by the toluidine blue-molybdate (TBM) method can be divided into four groups. The first group is resistant to the action of dilute ribonuclease (RNase) but is sensitive to deoxyribonuclease (DNase) and consists of both types of chromosomal RNP, perichromosomal RNP and intranuclear amorphous parachromatin. The second group is digested by dilute RNase and by DNase, and consists of the amorphous parachromatin that diffuses into the mitotic spindle and the nucleolini. The third group is digested by dilute RNase, but not by DNase and consists of both types of diffuse cytoplasmic and the granular cytoplasmic RNP. The pars amorpha of the nucleolus constitutes the fourth group which is resistant to digestion by dilute RNase and DNase.
2. Biochemical and other studies indicate that the effects of digestion by the enzymes is not due to contamination of RNase by DNase or vice versa.
3. Staining of chromatin by TBM (method C) is usually due to dye-binding by RNA and DNA and the intensity of staining is reduced by treatment with RNase. When the effective concentration of dye is low only RNA appears to be stained; digestion with RNase then leads to an increase in the intensity of staining. It is suggested that RNA may sterically mask the phosphoryl groups of DNA. A method for selectively staining RNA in the chromatin and chromosomes is described.
4. The observations suggest that the chromosomal, perichromosomal RNP and possibly the nucleolini and intranuclear parachromatin are present as a DNA-RNA hybrid. Current knowledge of the nature and enzyme susceptibility of informational RNA and its DNA hybrid suggest that the major component of the hybrid stained by TBM is informational RNA and that this type of RNA is present in the amorphous parachromatin of the mitotic spindle.