Differential Staining of Nucleic Acids

Abstract

1. Thionin, being a basic dye of thiazine group, stains DNA and PNA of the cell differentially in blue (α) and purple (β) respectively.2. Metachromasia of thionin ' can be observed in vitro by mixing solution of the dye with various amounts of nucleic acids of whatever type. When large excess of nucleic. acids is added with small amount of thionin, the color of the solution is blue (α); increase in the amount of the dye in comparison with that of nucleic acids causes gradual change of the color taken by the solution from blue to purple (β) and finally precipitate in the latter coloration appears.3. Marked metachromasia caused by nucleic acids in vitro is shared by toluidine blue and cresyl violet, but metachromatic staining of nucleic acids in situ with these dyes can not so readily observed as with thionin., 4. Either of the α- and βcolors taken by these dyes can readily be distinguished from the metachromasia caused by mucopolysaccharides (γ-color).5. Staining of nucleic acids with toluidine blue is partially inhibited by the presence of sodium chloride in high concentration. Thionin-nucleic acid complex can be dissociated by saturated sodium chloride solution in vitro as well as in situ. These facts suggest that nucleic acid stainings with thionin and toluidine blue are of electrostatic nature.6. Partial inhibition of the staining reaction of nucleic acids with thionin, toluidine blue, or cresyl violet by different means gives rise to PNA stained in a-color, which otherwise stains in β-color.7. On the basis of an experiment using histone and DNA, the a-color of thionin taken by cellular DNA is assumed to be resulted from competition of proteins for binding DNA. No such evidence was ob-tained with cellular PNA.8. Implications of the metachromasia of some basic dyes caused by nucleic acids and of the ints ference of proteins in nucleic acid staining with basic dyes are discussed.Acknowledgements. It is a pleasure to acknowledge my indebtedness to Dr. O. Itikawa for his encouragement and to late Miss. H. Kawata, Miss S. Takeda, Mr. T. E. Yukimura and Mr. O. Harikane for their assistance.